Well, it all depends on how much pressure you are running and what size tip you are using. Pearls/metallics generally need to be thinned more than standard colors. What I do is take a new bottle of paint, open it, and fill it the rest of the way with water. That sprays nicely through my HP-C on about 40 psi.
Back the flourescent colors with white. Back the fascent colors with silver. As for the faschange, it depends on what you want it to end up looking like. That paint is pretty transparent. It will give a purple tint to whatever you put behind it. I like backing it with black or white. Silver doesn't work very well. You lose a lot of the purple. Try backing it with the fascent blue. That gives a nice effect. Basically, the part sprayed with faschange will be the color of what you back it with, but you will catch hints of purple here and there.