Painting with modern paint systems is much more complicated than it seems at first glance.

First, go to this site and read the two articles under "How To" about preparing fiberglass for painting.

http://www.wescottsauto.com/site2003C/frame_specs.html

Then decide what type of paint system you want to use, and follow their instructions. I use Sherwin Williams basecoat / clearcoat system, and they are very specific about how to apply it.

If you're using basecoat/clearcoat, you typically DON'T sand the basecoat before applying the clear.

Also, unless your fiberglass body is totally gnarly, there's no reason to coat it with bondo. You just sand most of it off.