Okay I've read through the comic pages you posted and I've some feedback for you!
So, I'll start with the art, since that's what you're most concerned with. I'm going to break this up into portions for the sake of ease.
Characters: The anatomy trouble you are having here is something that happens to a lot of budding manga artists. If you base the knowledge that you wish to gain on cartoons alone, you'll struggle with anatomy. The reason is, if you have a grasp of figure drawing real life people, you develop the ability to memorize human dimensions and call them up and shape them according to style, but knowing the basics first will always be key here.
In the case of your characters, you were right that the anatomy fluctuates. The eyes move around the head, the character's dimensions don't stay consistent and I can't actually tell Paige or Eunice's heights respectively or in regards to their environment, though this problem is two fold and I'll explain that later. So, here are some guides that I've found helpful both in drawing from life, and making cartoon characters. First off is Figure Drawing from real life. The tutorial I'll provide will give you an idea how to start up a figure drawing and takes you through a bit of the process. It does show nude models in the drawings so, if that's not something you're comfortable with you don't have to use this reference (however most figure drawing classes/tutorials use nude models for reference).
Here's a tutorial for figure drawing cartoons which deals a lot with expression both with the face and withe body. It's not manga based, however these techniques are easily modified into that style, so the framework holds up. I'll also share this resource for facial proportions because, believe it or not, even cartoons need to have a certain measurement so the faces can engage your audience and this vid is pretty explanatory about them (as well as shows the process).
Oh! Also, hands. You need this tutorial on hands.
Shading: With grayscale art it can be hard to tell where the light source lies, this is just one of those things you have to be aware of, since your audience can't really tell on their own. In your case, not only do I not know what time of day it is, but the shading on the characters has no discernible source, so it's all a bit random and in convenient directions for depth. Now, your drawings do look more rounded out with shading, however, the inconsistent light source makes the shading you do use a confusing cue for a reader. So, I figured I'd drop this here. This informative piece explains shading and it's affect on artwork and how others perceive it. Not only that, it explains how shading and lighting work in tandem against surfaces and other objects, so it's a good start for really getting the depth out of your piece, and making it pop.
Backgrounds: Remember how I said that the trouble with Paige's and Eunice's respective heights were two fold? This is where we get into that part. Backgrounds have a huge impact on the size of your character, so understanding backgrounds will also help with height and proportion issues that can crop up when you design a scene. To that end, here is another resource about establishing backgrounds and how to construct them from the ground up.
Also, when establishing backgrounds you have to take shading and time of day into account, so these two things help each other out in making a scene really shine. This also leads into perspective (as this will make your scene have depth). You do run into the issue of perspective not making sense with regards to the character model. Case in point: This page. I know it's supposed to look like she's reaching down to grab something, but instead her arm and her body just get wider. Without shading I actually thought that this was a mistake in anatomy before I realized she was reaching. Now, foreshortening is kind of a pain, so don't worry! You're not a bad artist just because one instance of foreshortening didn't work out. This takes time and practice, and sometimes you have to study lots of figures to get it right. However, it's worth it and it buffs up your skill roster plus gives you the power of dynamic poses!
Now, you also have a lot of white in your backgrounds, so much so that they feel unfinished. It also makes your art become flat so, I don't really get the sense of depth from the environment. I'd say, learn about clouds, environments, weather, so that your scene feels fleshed out and solid.
Action Sequences: I'll be honest, I had a hard time understanding a lot of the action sequences. Now, these are tough all the way around so, you're not the first person to struggle with these, everybody does. In Eunice's case, I can't tell what's happening a lot of the time. Now, with perspective, backgrounds, and shading combined they can almost completely turn this kind of problem around. However, there are a few points I'd like to make here so you can see what I mean. To start, this page. Eunice uses her power to fight the slime monster, however in the second to last panel, it's just indicated to be bright. I actually don't know what power she used, (though I know her power is illusion, what illusion did she use?) though I decided that it had to be a blinding light of some kind. From the illustration I just couldn't tell.
What I'd recommend is that you think about how you want to represent some of the more formless illusions like light and darkness. It can be done, but it really helps that we the audience can tell what happened. It's also hard to tell what is happening in the fights themselves and again, perspective, backgrounds, shading, they can all help fix this issue. That being said, I'll leave you with this video about fight scenes. It's just a simple tutorial its not crazy detailed.
Okay, so that was for the art. Now, I noticed a few things about the actual comic panel construction, plus dialogue and narrative issues and I'd be remiss if I didn't make you aware of those too so, let me break up that section as well.
Story: Story wise you're off to a good start, we've got our main heroin in the world she's been set up to save, starting her quest a little on the rocky side. This isn't a bad way to start, however there are a few things that stuck out to me as distracting. First thing was, it felt a little out of place to throw in the "You have to save two entire worlds" from the very beginning. Since there isn't really build up to this point (since we're in the beginning) it doesn't really grab me. The first thing I thought was "Oh, the chosen one. Got it." and whether or not this was your intention, I actually didn't feel invested in Eunice because she was handed her power, and handed her 'get out of jail' free card by being saved and all in the span of a page or so. Now, that's not to say that a story can't start in medias res with the character already having her purpose.
However it'd feel more natural if we started directly with Eunice without having the meteor and the distant stranger giving her a quest. It's sort of the same advice I give novelists: Start your story in the action. Since you won't get the chance for massive build up yet, putting us in the action with Eunice, like say, in the middle of the battle after the map was torn apart, we'd find her in this desolate, hopeless situation with a stranger. And her interactions with Paige, with the world, could tell us about her and that a vague air of mystery can keep us drawn in. She's intensely looking for something? A goal that she bides behind a determination whose source we can't know, yet there it is? That kind of thing. We could learn piece by piece what happened to her and THAT is where your strongest build up can happen, plus, it can also reinforce the friendships she makes as we, the audience, are also a stranger to Eunice.
So the info-dump in the beginning about her being a world savior destined to...well world save, is a bit heavy and without the kind of punch it really needs. Since you're in the beginning of your story, this is an easy fix. Now, I know these are novel resources, however, writing is writing, and you can adjust for medium as you go. Here's 10 ways to start your story, and Character building. These can help you see narrative structures that'll help give your story a kick. I'll also caution you about random events and occurrences.
When we start with Eunice we actually have no clue where she is, since we start off with her floating in a panel, then we realize she's in town. A handsome man shows up, and girls gather around him. Eunice, without any idea what Obsos is or who, decides that this random handsome guy on a horse could be Obsos, so she causes a mass hysteria in order to end up with her key item: Map. Now, this for me really didn't make cohesive sense. Why would she just break out into a crowd and cause a mass panic over an unfounded assumption? I know she's 14 but, when I was 14 I lived by the rule of: If I throw a punch, expect one in kind. 14 year olds are smarter than often they're given credit for, so having her randomly attack someone without probable cause, only tells me as a reader that this specific person needs to be attacked so she can get the map. He then disappears from the story.
Now if this was a kind of foreshadowing, what you might do is indicate to us, the audience, if this guy is actually a retainer for Obsos, if Eunice can sense if someone is Obsos or one of its minions, etc. Because without establishing this, the entire first encounter makes no sense. It just happens because Eunice needs the map so she can meet Paige. I'd take a look into your story structure and see if there's a better way you might introduce this item that also gives us hints or visual cues that it may not belong to the man who carries it, because up until Paige said so, I had no sense at all that this guy was shady (hence why I felt the fire tornado was an overreaction on Eunice's part). In regards to Paige, after the fight one thing derailed me from the story was this bit here. More specifically this quote: "If I have to fight her again I won't go easy this time..." I can't tell you how many anime shows and manga issues have someone saying this line.
So, while I'm not proud of it, I've been in scraps. Thing is, nobody ever said anything even remotely like this before or after a fight. Sure there was a lot of BSing sometimes like "I'll kick your ass" or whatever, but nobody I'd ever seen nor scrapped with, said anything of the kind at any point. I know that anime and manga reuse this "I won't go so easy on you!" line, but it's actually a devaluing line. It makes the moment feel cheap and more like the character saying it, has nothing behind them but words and a puffed up chest. It makes me less likely to believe that a character has anything interesting to show me at that point, because the line itself has been so overdone across the board, it can be viewed as a narrative crutch. I'd recommend you watch out for tropes that could hurt your narrative. It's not to say you can't use them but, some can be incredibly distracting and derail your story.
Pacing: Pacing can also get rough, because it's hard to know when something is too little or too much. This narrative sense is something that comes in time with practice. That being said, there are a few things that can help you sure up your pacing: make an outline of your story and decide where your most important moments will happen and how you need to get your character's there, while still having the story make sense. Case in point, we get a very brief introduction to the destruction of Eunice's world before we're thrust into a random town for the first encounter. This felt all too brief (which is why perhaps starting in the middle of the fight with the slimes and meeting Paige could be a good thing, because it gives us something to learn about Eunice) and glossed over. Now, I've no doubt you'll elaborate on things later, however, since you're going to do that at some point any how, having it all so briefly mentioned before moving on almost immediately was too quick.
In what felt like a few narrative seconds we moved on from one scene to the next. I think I know why it all feels so brief, too: you don't use establishing shots. Again, I didn't know that she was in a town to begin with and the first chance I got to realize that we were thrown right into the pretty boy scene. It'd help if you establish where we are: a forest, a town, etc. With a picture or a cell all its own. That way, you establish the scene and the reader can feel like they're part of it.
Panel/Speech bubbles: This one is a relatively simple fix. You have chunks of dialogue that covers a lot of your panels. Now, not all of them are this way, however, sometimes your speech bubbles get a bit large and I feel like the character in the scene is fighting for space. This page, again, is a good example of this happening. I feel like the action of the scene has to contend with the long blurbs of speech. Now, that's not to say you can't have a sprawling narrative, but finding simpler ways to convey feelings, or visual cues that can do the talking can really up the ante in terms of your story. I'll use an example from one of your own text bubbles on that page (I'll use the larger one).
Original: Why didn't I realize this sooner... this world I was sent to... it can turn to chaos...
Edited: Chaos exists even here.
See how I said the same thing as you did in half the time. We already know she's been sent to another world, we don't need her to reiterate that. It comes off as the author believing the audience isn't catching on. Now, I know this was not intentional on your part, but that's how it comes across. Also, you'll notice I left out any of your previously used ellipsis. You're overusing them. On a single chapter page you used "..." 32 times. Ellipses are not periods, they don't end sentences in the same way. Now yes, in comics they do get a little more leeway, however, overusing them creates two problems.
The first is speech bubble stretching. You need to make the speech bubbles larger to accommodate the longer sentence, made longer by using up to three ellipsis' per speech bubble. Since one of your issues is that your speech bubbles often contend with your art, I'd recommend ditching the ellipsis altogether. Second, since an ellipsis is more than often used as a way to express omission, it means that your character literally stops at the end of every sentence to... well, that is to say she doesn't finish her sentence. It creates awkward pauses in the narrative that don't make sense. So, until you get used to where they go, delete them. This will tighten up your story, shrink your speech bubbles and solve three problems all in one go! (And don't worry, ellipsis are tricky buggers, lots of people get confused by these so, you're not alone in that at all. Have no fear, it happens to everyone!)
Hahah hoooo boy if you've managed to make it to this paragraph, you are awesomely patient. I know that a lot of this feedback can be overwhelming so, I'll give you the best advice for handling it: one piece at a time. It's all right here in one place for you, so you don't have to feel like you've gotta do all these things right this second and be master class, A+, superstar. These resources are here for you to use at your leisure whenever you need them or have questions about doing something. Invoke them when you feel you need them and most importantly: practice. You're going to improve, because you make art and each time you create a new page or make a sketch you're learning. You're going to get where you want to go and you don't have to feel like you need to be there right now. Whenever you need to, just take a gander at what's here.
You've got a story in you and I think that if you keep going every day, your story will blossom and you'll make work you can be proud of. You should be proud of what you've already done, because it's going to belong to a larger body of work AND improvement. The improvement part is just inevitable even if you didn't have resources, because with every pen stroke, you learn. You've put your comic out there, you've made something you enjoy, and others will too. I wish you the best of luck in this, I know you can do it, you're already on your way. 
