Ricardo,
I use only a little bit of primer on the seams that always need to be filled and sanded smooth. I used Klass Kote white Epoxy primer, but there are a lot of good ones available. PPG makes a good one for fuselage work.
I am just getting ready to shoot the clear. I have been using (and like) House of Kolor Kosmic Uethane Show Klear. Excellent product with great clarity. Clarity in clear coats is something a lot of guys don't take into account. Most guys think clear is clear,,,,but it may not be all that clear!
http://www.coastairbrush.com/products.asp?cat=756