Lots of people are making posts for, quote, “Twitter refugees” that explain a bunch of stuff about setups and such. RedLenai explained most stuff, but tags! Basically, tag as much as you want but only stuff that’s relevant (like, don’t tag “dinosaur” in a bread recipe) but also you can monologue in there! Most people block bots so make sure to change your picture and reblog things so that people know youre a human. Also follow Neil gaiman, its mandatory (it isn’t but do it anyway)
these r on my page but not my posts but they cover some good ground in terms of site nav, posting and some other useful things
as for themes uh...explore, experiment and read the guides theme creators leave coz they tend to cover most bases in terms of how to edit them to your liking within their terms. that or feel free to make you own (don't ask me how idk)
another tip for tags is that the first 20 i think are the ones you can search so try to keep your most relevant at the front and also consider using em to help navigation on your own blog if you decide to keep reblogs and your own stuff on the same page (i think the last post covers that one)
I kinda wish I had my my art blog as my main blog when creating a tumblr rather than having my comic blog be my main blog.....ah shit 
there's still the opportunity or ability to change it in the settings (i forget which coz it's been a while)
but it has been useful for me to have different sideblogs for specific stuff like fandoms or rambles and other stuff since i feel like it both helps keeps my posts in order but also kind of keeps me organized so all stuff related to x thing can go in one blog or the other or be shared between whenever needed
apparently you can do that by changing the url but it doenst seem to be working for me. At this point I feel like it would easier to just delete my account and start over which I dont want to do.
Also, does tumblr have an algorithm similar to instagram and other social media sites? (Posts made at 10am-1pm gain the most traction)
logging in to check how to do it coz it's dirt brain hours but i'm p sure it's simpler than this will edit when i have the answer
edit: officially there isn't a way to do it but this sites "long way" seems like a decent option
if i'm not mistaken i think it's what i did when i was trying to sort out main and side blogs in terms of the whole swapping urls and then redirecting ppl where were following to go to the other one and then switching posts over
tumblrs own export function may work but tbh i've never used it nor do i know how 
tumblr is free from the so called algorithm or more accurately just doesn't operate on one like those other sites. posts from a decade ago could show up on your dash with the same relevance as one from ten minutes ago and it wouldn't make much difference
i have heard that stuff posted on gremlin hours (so like afternoon night time) and especially on the weekends do well but honestly with proper tags and enough reblogs things can take off on their own
but like in general you can post whenever and there isn't much difference and it's not really meant to be stressed either, just go ham 
You've only posted... like... barely anything to be honest, so you can simply change your account name, create a blog with your Series name and then start posting your series content in there. You don't need an impeccable, flawless blog, a lot of people start that way and then switch things or get organized in the long run.
Don't be afraid of making mistakes, not tagging stuff "properly" or whatever, nothing will explode (Not that I know) also you're learning so cut yourself some slack and avoid trying to nuke as a solution.
And regarding your question about the algorithm, here are a few answers to that:
A small explanation by laptoparmageddon
the bare bones is always "likes are like a bookmark, reblogs are what get posts moving and tags is where the conversations/replies are happening"
on most platforms its the shares that get things goin and tumblr especially relies on the community/ecosystem all workin together to sustain itself (something i think i'd share on the side and not the main purely for language in the post but yeah)
So if you reblog other people's work, your work will get attention then? I think thats what Im getting from this and in that case, I really hope its not as bad as artfol.
Also I did change the names of my blogs so now my "primary" is given the secondary title and my "secondary" is my primary. I could just nuke the content on both and reupload them on the opposite accounts so that my primary is actually my "primary" but I've always been anal about deleting shit....I guess I just have to deal with it? I dont know. I can make this work I hope
If you reblog content from others, that's how they get their content seen. If you want to get your stuff seen, you gotta encourage others to reblog it. Again, there is no "algorithm", so it is basically team work. If you reblog something from another, that'll another will be benefited by being seen by those that follow you, and viceversa.
I don't understand what you mean, you can edit the name of your account, blog name, content entirely, you can delete posts if you want to clean everything up without nuking the account. I don't understand what are you struggling with.
Edit:
I just saw the fact the your first blog is your main one and got annoyed with myself over not realizing that until it was too late. Because now that one has a star next to it that says primary and I guess that even added to my annoyance with myself. Also, I take that reblogging is the equivalent of retweeting?
It’s how you get things to be seen, when you reblog something all your followers see it and that’s the only way to make people see it pretty much
Then you can simply change your username, keep the posts, make a small announcement to redirect to your comic properly (You can delete posts too if you like, this ain't twitter)
And yeah, is not that complicated, it functions exactly as retweet or simply as sharing something in your profile on facebook. Still, no algorithm, don't go around thinking that because you follow/reblog/like something that'll increase your chances to appear as a recommended blog, or your post will be seen more or appear in someone's feed.
It's all pretty much what I and others have explained already, not hidden magic or formulas
After reading this thread I'm curious: How does that work with zero followers to begin with? Hoping a person you reblogged does you a solid and returns the favor?
Basically, is like making friends in the real world.
You start first checking stuff in Tumblr, see what you like, meanwhile you post your stuff, then you eventually find something you like then follow it, you reblog it, interact with it, then you start chatting around with the other bloggers whose content you like, either provide to the OG idea, add a joke, or exchange opinions, whatever.
I don't think engaging for the sake of expecting favors works, basically those are ulterior motives and if you only focus on that, then you'll likely end up in a "nice guy" situation.
Personally, I simply didn't care about engagement, I saw posts from my favorite fandoms then began to interact with the posts, with the previously mentioned. Most of the people that follow me on Tumblr, mutuals mostly are into the Supernatural fandom, obviously, my non-SPN content is not touched by them, and I don't expect them to interact with it, I know that I'm out of touch with the webcomic community, but the same method applies too.
So of course, you can try and be as interested as possible with the hopes someone will "return the favor" or get interested in your stuff after seeing you in their notes quite frequently, and maybe a mutual interest will be generated, but... yeah, Tumblr is like friendship.
I will admit that the platform seems very fandom focused. If you have zero interest in doing free advertising for a company's IP is there a place for you there?
I'll go digging around. Maybe I'll find my tribe in some dark corner there.
We can dance around like the bee people in that No Rain music video.
Of course it is, as I previously mentioned: Tumblr works as a friendship that starts with a common interest, it's a mutual interest that needs to be born in order to build something up. Bust just because you're nicely reblogging stuff, commenting or similar doesn't guarantee people will be as equally as interested, that's why focus on it being genuine, and not a shallow relationship to obtain something in return. Aka an old version of the sub x sub.
That interest can be anything, "Art" can be a fandom, "webcomics" can be a fandom, "Original character" can be a fandom, literally anything. The thing is that you have to engage, you have to go back to your early stage of being that kiddo who just got access to the internet and wanted to interact, consume and engage with everyone and then someone would come around and be interested in you as well.
There are a lot of artists who post original content too, some have been there since I was 13.
really the two keys to posting art is 1. knowing how to use tags, and 2. having a dedicated art blog
This is from cozylittleartblog
tumblr only tracks the first 20 tags on a post, everything after that is Just For Funsies. tracked tags will show up in search, both for the whole website and on your blog.
if you're not sure what tags to use, see what other popular posters are using! i think i mentioned this in my tumblr guide post, but generally you want to tag fandom, characters, ships (if applicable), and any AUs or similar things. oh, and content warnings if those apply, too. then if you want you can try stuff like mediums and other general tags, that'd be your #art, #illustration, #fanart, #fanfic, #digital art, #(program you used), etc etc. you don't really have to use those, but if you want to keep your blog Super Extra Organized or if you're posting original content with no fandom tags to lean on then they are good options. (you can use things like #ocs, #original characters, #character design, #concept art, and genre tags for those!)
If you consider that you should gatekeep your feelings of what you like because you don't want to """""do free promotion"""" then... you won't succeed either when it comes to other people's work, other people's content be it they are new, veterans, unpopular, popular, etc.
