I have a realistic project I want to do and plan to make as soon as I get the things I need, but once I transition from that one to this one i’ll still have these questions to deal with in that story.
scale creep is so real. I deal with this pretty often when I try to work on my other projects. I think the thing is if the world ends up bigger than the one you have on paper then either commit to giving it the room it needs or accept dialing it down. The worst thing you can do is not give the story breathing room if it needs it, because that's how you end up with too many loose ends. If you love it that much, then you should commit to it.
The reality of graphic novel esque series is that you are just gonna learn how to work faster or accept that it might not get done any time soon (on average, most manga artists take about 10 years or more to finish a series when they are working full time). You wouldn't even need to work at breakneck speed like that, because the webcomic sphere is naturally used to sporadic and slow updates. But a few pages a month is not really sustainable unless you're really alright with that.
Make the other one first. You will understand so much better how to plan a feasible project and how long things really take and stuff once you've made a comic. Jump in and make the small thing first and then plan the bigger thing based on the stuff you learned making the small thing. I guarantee, if you plan it all out now, you'll end up re-planning so much based on your experiences actually making a comic that it's probably more efficient to just leave the planning for now.
It's really easy to get sucked into endless planning of big projects and for it to become a distraction from actually creating things. You can't plan for all the problems you'll come across by asking other people; you'll learn so much more by making the mistakes and learning from them for yourself, and working out what sort of methods and planning work best for you.
Yes, and I'm saying that you should stop fussing over all the planning on this other thing before you've made that one, and just make the simple one first, because what you learn making it will impact how you make the other one. A lot. Take it from somebody who's been making comics for over a decade.
Does it have to be entirely a comic? With that many characters, maybe parts can be in novel format which will update faster and be written faster. Comics take even longer than the estimated time because you will end up having life happen, you'll get sick, have to do other jobs, like stuff HAPPENS and so that 48 years will be like 50+. So consider novels, using the most visually exciting and impactful arcs as a few comic arcs that can be standalone.
By your own admission this is not a realistic goal. No story you are thinking about should be 48 chapters if you can only do one a year. No audience will hang around to read that. You need to simplify the art to where you can do an episode in a month max. Even at that, that's 4 years of work. Truthfully, unless you are a seasoned artist with writing experience, this also should not be on your list of comics to make. Start small. Finish some shorts. Get some experience. You don't even know what you don't know right now. Leave your magnus opus until a later date. You have time.
Their arcs rely on meeting the other main characters at a certain point in those characters lives and stuff.
I could kind of get one page a week back when I drew stick figure people on single color backgrounds or copy paste buildings that were just squares, no clothes even just sticks and a head, background extras being just circles on sticks. Now I want them to be people.
How do I make the art style more simple than it was before?
Since you want to make a comic... Start with a question if you will be able to pull it off at the level your art is. At least how close you are. Because if you believe your best art at the moment is stick men and you don't like stickmen but want your comic look like an issue of Batman, you would really want to start with something short to learn how to both write and draw.
I don’t want batman, I just want not stick figures. I can draw humans decently enough I think.
What I want to know is how to simplify my style more so than the stick people, since it took a year to do the stick people version.
For projects where i need a higher level of artistic skills than what i can currently pull of, i hire an artist or more (like an artist and a colorist).
Even if you go that route, knowing how to draw well enough to explain clearly to your artists the visual concepts you are aiming for can help a lot.
If you don't have the money for that yet, you can try to save up and set a budget to hire people. How hard or easy it will be will depend on your financial habits and situation. But if you are able to save some cash, you can stockpile enough to hire people.
If you decide to do the art yourself, you can practice and focus on different aspects. If you need a specific style sometimes a book that teaches how to reach such style can help wonders. Personally i recommend books that teach artistic principles.
How do I make my process simpler and faster than it is.
My process was:
draw squares with the fill tool to match my general plan. Those are the panels
Add the characters by scribbling and smoothing out stick shapes, then paste on the head, drawing a face on it. No height chart. No nothing. Do whatever.
Add like copy paste assets and a few rectangles to make the background if even that much.
If you can’t draw it trace a picture of it and make that a stock asset.
At this point, I think the best approach is to save the project for when you can hire other people, whether out of your own pocket or via having a good enough reputation as a creator such that others are willing to contribute money and/or time to make your story happen.
No amount of training your speed or simplifying your art is going to result in you getting this project finished in less than 20 years, and your wrists will probably not thank you. And that's not including the time you'd spend training your skills in the first place 
But that's what it's going to take if you don't want to compromise your vision :] In the meantime:
- Do some other projects that you genuinely care about for their own sake. The goal here isn't to train your skills to do this big project, but to build your reputation as a creator so that other people are willing to help you do this big project.
- As for your big project, for now, make it a 'sketch of your vision'. Basically, a less labour-intensive version of what you envision to be the final comic. This could mean a novel, or a stick figure comic with super-quick but unimpressive art. The first version of your story that you put out isn't necessarily the version everyone will remember; see One Punch Man
So what could I find? Every other idea is like a full thing way too big for me as an individual artist.
Like I don’t have any real small-ish ideas that I can draw in under a decade.
Like, if I have an idea for a movie length story, that’s still like 5 years of webcomic drawing. And most of my ideas are at least longer than that.
I invented a small idea earlier but i’m not sure I like it actually.
I feel you on the gigantic idea, but the reality is that as a single human you are absolutely constrained by time (i.e. your healthy life span) and there isn't a way around that. Your only options are a) write the story as a web fiction (significantly faster than drawing), b) make it your full-time job so that you can devote full time hours to making the comic and work at a pace where you can finish the story before you die or c) get a well-paying job in an unrelated field and hire a full-time professional to do the drawing for you.
There are a TON of short cuts you can take to reduce time per page (which have been detailed elsewhere), but even with those tricks, you would still need to spend hours per page, which circles us back to the sentence above. There aren't really short cuts to long stories.
Personally, I went with option A while I work on shorter projects and build publisher connections, then maybe in like a decade I would have the necessary health and options to dive into the longer story (if I still want to, that is. I'm quite enjoying writing single books right now).
Everything I work on is long running, but I'm a novelist so I don't need that much time to complete stuff. Can you write complete story as a webnovel and start working on the comic little by little till you get an artist who's willing to collab with you? Like how Tbate used to go, I think the comic still hasnt caught up with the novel despite going on for years. If you have a good story and a big world that is good the way it is, then why change it? If the world-building is not essential to the story and its more character driven and not plot driven, then you can cut the parts that don't really help with what you're going for. I have a series called Lawful/Lawless I want to launch and the huge world-building and the hundreds of characters that come in whenever in diferent arcs, and the endless worlds and different places is the thing that makes it good, so I'd rather have it take a while than to rush things