It's not really an au question but I was wondering if you had any tips to stay motivated on a big project like this. I can't seem to stay motivated on anything for very long, even if I still want to and have plans to work on something I can't seem to actually do it.
Hmm.... Here's the thing - executive function is a habit. It's not a talent, or something you're born with. (Some people have trouble with it, due to ADHD, for example, but even neurotypicals don't automatically know how to work on something long-term.)
So you should think of your ability to do long-term projects like a muscle. It has to be trained!
If you try to just start a big project with no training, imagine yourself attempting to deadlift 400lbs with no prior experience. Either you'll fail, or you'll hurt yourself because you don't have technique - you'll get burned out.
I was originally ALSO really bad at long projects. I would think up huge things for myself to do - novel-length stories! Multi-volume comic tales! Entire card deck illustrations!
And then I would give up having not even gotten halfway through, because my imagination was bigger than my ability to stay focused.
You have to start small. You have to reward your brain for accomplishments. Set small goals, finish them easily, and pat yourself on the back. Draw a small 5-page comic that isn't going anywhere else. Write a short story, edit and finish it and set it aside!
Years down the road, someday, eventually, you'll find that you can draw the same story longer, that you can stick with a plotline for months on end. You'll develop your long-term-project muscles and get better at it!
I'm STILL not perfect. I have been with WD!Steven for 2+ years, and it has taken legitimate effort to turn myself back to it. Not because I don't like it, but because the human brain naturally likes new, shiny ideas more than old ones it already knows a lot about. (That's actually a good thing - that's how we evolved to be where we are. Exploration of new concepts is a natural tendency of the human brain.)
Anyway, I hate to be pedantic but.... it's honestly just practice. Lots and lots of practice.