Depending on your vehicle there are companies out there that can supply you with a do-it-yourself upholstery kits, of course you need to be somewhat handy.
Pretty much any auto body shop will paint your car. Since they give free estimates, you can take it to different ones to find which one will you the best price.
Yes you can in most states. The process is complicated. The main test here is if it passes safety inspections after it is running.
I assume you are referring to a vehicle made of preexisting parts,...
I have re upholstered a few boat seats and will offer what wisdom I have gleened. If we are talking about single fold down seats, it's probably not worth the effort. By the time you buy your material...