Gary,

I would say white primer such as Klass Kote is an excellent undercoat for light colors on top. But use grey if the colors are dark. Silver covers amazingly well and results in a very even color to shoot top coats over. It also can be used as a highlighter of any surface flaws. Repair prior to top coats is the simplest way to do it.

silver prior to yellow on my wing project resulted in about 15 - 20 gram weight gain per panel which is for yellow, is not bad. I don't think I'll do yellow base again