I guess I could attempt something like that.
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
There are many ways. First thing you can do right now is to write a summary and test it here in the forum.
So the premise is that the main character grew up thinking he was going to be the chosen one but years later he’s still not. He still expects to be the chosen one one day.
Then one day he meets the real chosen one. The real chosen one is apathetic to the world, only trying to save it because he’s destined to, and expecting to fail.
But he can’t do anything about it, and if he tells anyone this will cause chaos. So he has to keep the secret and be a fake chosen one who wishes he was while accompanying a real chosen one who wishes he wasn’t.
How does the main character want to save the world?
How can the chosen one save the world?
Why does it lead to chaos?
Yeah, I won't deny it's hard to find a small idea you care about; there's a reason just telling us 'do a small comic first' doesn't turn us all into functioning creators overnight even though it gets repeated so often XD
The best advice I've got is these:
(ideas for shorter stories that you ... might have a higher chance of caring about than some random unrelated idea)
This might not be very helpful if the only reason you care about your long story is because it's a Big Long Epic Saga and you always thought it'll be super cool to create a Big Long Epic Saga (which is valid, that's how I started off when I first tried to make a webcomic :P) - but if you love your long story for other reasons as well, it makes sense to make a short story that shares those same traits you love 
(other short comics to reference if you're struggling to fit stories into very few pages)
Sounds like you'd want to write a long novel, and get it popular enough so that other people are willing to help you adapt it into a long comic :]
I guess I could make a spin-off of my main story, exploring a certain small part of the world in detail.
It could probably lend itself to a pretty great story.
He has to unlearn the serious emotional abuse he’s experienced and stop considering himself solely responsible for everyone’s problems and let people in.
Also his role at the start is to be the big face of the chosen one stuff, he saves people from villains and stuff. Then he fights an evil king and stuff and destroys the monarchy.