Since the DGS wants cars, IMHO, use the red, then the cars then the others. since you will need to change to proportions as you go out, put the cars on 2 side of the star. I just made an elaborate CS variation, with a red band around the star. I boxed in the 2 side pieces with the same red, then added my other borders. I think it worked quite well. If I were doing it, I might make diagonal pieced cars for cornerstones. I suspect whatever you do it will be greatly loved.