I have my doubts as to whether 4 high school friends all going in on something this big will end happily. Granted, that's the same advice my dad would have given me when I was your age, and the same advice I would have ignored when I was your age thinking he was an idiot. But at the very least make sure you're all 100% on expectations and responsibilities. Not that I'm age-shaming you (lol... is that a thing? I bet it is). I wouldn't go in on something that big with 4 of my friends now. And I'm over 50
If you do go forward with your plan, you might want to consider - if you haven't already - approaching any auto shop, welding shop, and/or carpentry teachers you may have in your school and see if they'd be willing to use your bus as a teaching opportunity. I did this with a car I had in HS. I - along with every other student taking auto shop that year - worked to turn my hand-me-down small-block Chevy into a 12-second sleeper. And that was with 1/2 of the class stoned. I could have probably hit 11s if it weren't for our proximity to Mexico