Ok im a custom painter, and this is my latest custom job. Even on paint jobs this extreme, there is no reason to strip the parts to bare metal, plastic, etc. It would be most crucial to strip in places that wear the most, such as door jambs, door hinges, under hood, etc.....but as far as the entire car, its really unnecessary as long as the paint is in good condition. BUT, since its been painted once already, i would definately sand the shit out of it with 320 paper and seal the entire car