Re: build on the old vinyl floor or strip it and start fresh ?
I have 2 busses and handled both differently.
My first was a 1977 Thomas International. The vinyl and seams were all perfect. I put carpet right over top. Three times over the past 6 years I pulled up the carpet to replace, mopped up the floor, and recarpeted.
My 1982 Thomas International was a different story completely. Vinyl was bubbled, seams were short, and you could hear crackling under the vinyl when walking on it. I pulled it back and found rust and corrosion galore. I wire wheeled the entire floor, blew out the mess, and primed with Rustoleum Rusty metal primer (with a brush). Then I topped it with a coat of Rustoleum paint. Bought some cheap vinyl flooring, and laid the carpet over top. It's been a year now and so-far-so-good.
Both busses stay in a dirt parking spot.
I guess it depends on how far you intend to take your renovation. Mine's nice, not fancy. Carpet get's replaced often. It's a very comfortable and equiped party bus with bunks, sofas, storage, etc... Something that I don't have to worry about getting messed up. Industrial strength!!