Question 1 -
The gun you were asking about requires:
"This gun requires a 1/4" air hose with fitting and regulator, and a compressor producing at least 3 cfm at 90 psi"
It sounds like your compress or won't keep up especially if its one of the small ones designed for a nail gun. You have to remember that your going to loose CFM in the hose as well. My bet is you will end up with orange peel, spits and all sorts of other problems, based on when I had a compressor that wouldn't keep up with my guns.
Fill your gun with water and see how long you can spray keeping the fan dialed in, I'll bet it won't give you enough to make up a coat on a guitar.
For details on dialing in the gun, and oh yes that does make a difference, the september Rod and Custom magazine has an article on how to spray correctly. It was written by Valspar/HOK's technical instructor and paint superstar, Brian Lynch. Definitley worth owning.
I can't help you with cleaning the gun since I only use gravity feed guns. But make sure you are aware of how much paint is in the gun, when it starts to run low you will have all sorts of spitting and other problems.