[Vwdiesel] How much paint do I need? other painting questions

[Craig Osborn]

I am planning to paint my 81 PU this summer.  It is currently painted a dark
gray metallic (Saab color done by the previous owner) and I want to change
the color to VW Sunburst Yellow.
I will be painting it with my own compressor and paint gun.  I will have to
use a standard paint gun, since my compressor does not have enough output to
satisfy a HVLP gun.
My question is this --   How much basecoat paint should I purchase to cover
the entire truck including the bed and one extra tailgate?  
Do I need more than usual since I will be going from a dark color to a very
light color?   
What is the best type of primer to use where I have removed rust?
Craig