I am going to have to respectfully disagree with some of the other posts on this one. I have two corvettes that I have owned for the past 25 years and I have painted both of them. When I first started I got a book on the subject that did not recomend chemical stripping because they said it would hide in the door jams and come back later and lift your new paint off. Following their suggestion, I tried to sand the old finish off, and found it to be very time consuming, labor intensive, dusty, and was dificult to do without getting into the jell coat. There is a special paint stripper designed for fiberglass that I got from the body supply shop and it stripped all layers of paint and primer down to the jell coat. (takes 2 gallowns) I found this to work very well, and it was much faster than the sanding process. Before I started I taped the jams up to keep it out of the cracks, then carefully sanded those areas when I pulled the tape off.
Before you start stripping paint I would make a drawing where all your cracks are so you can examine the body to see if the body is craking or if it was caused by the paint film being too thick. If it is the body, you will need to repair this first before you paint it.