By shooting the whole car flat black first you end up putting a couple more extra coats of paint on the car. This can sometimes hide detail. Not really an issue with a body this size I think. Couple coats of primer, a couple coats of flat black, coats of color, coats of clear, you get the idea. Also how will you clear the body color ? if you remove masking you will have to clear the flat black. If you clear with the stripes masked you will end up with a big ridge where the stripes are. If you paint and clear the body and then shoot the flat black stripes I just think it will be much more easy. I may be missing something and I am not trying to tell you how to build your car so please don't take it that way. Just trying to understand why doing the stripe color first is better. It may be, I may have to try that if it works good for you. Also dont forget the trick of spraying the car with some clear after you mask the stripes. It will help keep paint for seeping under the edge of the tape. Looking forward to seeing your build. Sounds like a cool idea.