I've done a little painting on fiberglass and the real problem long term is adhesion of the paint. Yes, it must be cleaned to remove any release agents and sanded, but normal primer does not have adequate adhesion on fiberglass. Forget what it is called, but there is a primer/sealer that is made especially for fiberglass that you should use as a first coat before you start building up with sanding primer. After that, it's just like any other paint job.
About the type of paint, the base coat/clear coat paint jobs while giving the best gloss, are almost impossible to spot repair neccesitating a complete recoat of clear any time there is work done repairing chips and such. The strongest paint that is easy to spot repair IMHO is the catalized polyurethane paints like Emron. Emron is one of the most chip resistant paint and easy to spot repair.
And, what did I paint my fenders with you might ask, the same rustoleum black that I painted the frame with, so I can repair/repaint easily.