Well, use the primer that is made by the paint company your using, otherwise, they won't gaurentee the paint and there may also be adhesion problems. You should take the bondo out and put new in, if it needs it. For a paint gun, you should get a high quality gun, it really dosn't matter if it's HVLP, that stands for high velocity low preassure, it is basicly approx 20-40 % more efficent than a standard gun ( 75%-90% hvlp, around 50% regular ) but are gennerely more expensive. I bought just a high quality siphon feed for a mere 25 bucks. For the nozzles I'm not shure of the sizes but I do know that the larger nozzles are used for primer, smaller for paint.