Thanks everyone. All of this is very helpful.
Next Question: Does it make sense to prime the pieces before individual construction, then put them together, putty, and prime again? I'm practicing on a patrol labor model I have. Since there are a lot of moveable joints, I'm putting small parts together and then priming and painting. With some pieces though, it will be nearly impossible to prime doing it this way, as they will be covered by other pieces and be surrounding still other interior pieces.
My current thinking is not to worry too much about the interior joint pieces, and just paint them (no priming) since they will barely be visible. Then on the larger sections (legs armor, arm armor, torso), mask off any different colored parts, prime, then paint. And I'm doing this by assembling as small section (the foot for instance) then doing the priming, painting coloring. I'll do the leg the same and mask off any joints that can't be removed before painting.
This is all kind of hard to describe, did that make any sense?
Oh, and unless my original question got lost in the babble: Is it always necessary to prime a piece before painting, or for smaller, lesser seen pieces, is it ok to just paint them without the prime coat?
SpaceCowboy