Rustoleum flat black questions

Okay, well i bought a fiberglass widebody kit for my car and promised a few people i would take it to a show so i painted it flat black with rustoleum paint. now i have to remove it to start bodywork and get a real paint job. First off can i rough this flat black up and bodywork over it or do i have to completely remove all of it. if so what would be best way to remove paint off fiberglass fenders and aluminum doors. thanks
ZACH