Check with Roscoe he has had his with just the gel coat for several years. It is very simular to a boat. I painted stripes on mine and buffed the rest and it truned out very nice, some think it has been painted. I plan to paint it later.
As far as stages, I got the rolling chasis first, then motor and trans, then the body and interior. Reason for me was budget. Worked out fine for me.
I'm very happy with my choice.
Joey