I have to whore this because I'm involved with the site but
www.FFURG.com is a Star Wars customizing site... Everything there would translate pretty seamlessly to XD customizing though, so have at it.
Basically for paints, anything that cleans up with water (water based acrylics)... If your paint requires thinner to clean up, or you see that it's "oil based" enamels, avoid it. Testors model paint (plain stuff) is oil based... They have an acrylic line too, but I'm not fond of the durability of Testors paints. Oil based paints react poorly with plastic types used on XD figures.
XD figures (and FOV, etc.) are mostly comprised of polyvinyl or PVC plastic parts, and PVC's a plastic type that doesn't react well to all types of glues, plastic welders, epoxies, or paints. Rigid ABS or "styrene" is more tolerant of various paints and things.
Head to your local hobby shop, and look the paints over... If they're worth anything they likely have good stocked racks for Tamiya, "Games Work Shop" paints, Polly S, and Testors... Polly S is some good stuff, as is Tamiya, though Tamiya you have to thin down as it's a bit thick. Mix it with water to thin it down or buy their thinner if you wish.
Do your painting in thin layers... don't just try to get it done quickly. Painting, good painting, should take time, and coats.
Look over customs and get ideas of techniques to do detail like eyes (considered pretty tough by most), shading, "dry brushing", "washes", etc. You'll see the more you look at figures how a customizer's technique brings out detail and things. From there you may get into making your own water-transfer decals and things, or whatnot. It's all baby steps though.
For SW figures I started out doing really simplistic headswaps and very tiny repaints. I moved up to droid repaints because, as Hasbro's shown us, you can never repaint an R2-D2 figure enough. That taught a lot of hand control with the brush, and forced me to innovate ways to paint straighter (masking, using templates, etc.). From there I moved on to more and more complex stuff... I haven't done much customizing with the military lines, and honestly I don't even do much SW stuff these days because of time and money, but I'm always stocking up on fodder for when the time is right.
