Honestly, painting is the part that has me the most concerned. At least on the dome, there is only the blue. Pretty sure the white only comes into play on the body and the legs.
This is a little further than I have researched, but there are of course, many options on painting. Some use simple rattle cans of spray paint, others use very specific mixes of professional grade paints, and the newest camp is using a product called Dykem. I've only scratched the surface on the topic of painting, but am already leaning toward the Dykem solution, because it is supposed to provide the most screen accurate color both in person and in photographs and video which may be taken of the droid.
As for "just the right blue," there is something called "hypothetical blue" as well as "hypothetical white" which many builders go after. It was proposed by one of the original SW prop builders (unsure of name at this time) who is a member of the builders board, and proposed this mix. I think it is called hypothetical blue because he wants to avoid any litigious issues with Lucasfilm. So it's hypo blue and hypo white for short.
Still, I'm leaning toward Dykem.
My major issue is it is very very dusty here in the desert, so I'm sure I'm going to have to build some type of painting booth with an air filter and reverse pressure to pull the air through.
Fun times...