Hmm lets see here!
1. Acetone is perfectly safe to use on the FACES of monster high dolls. It's the bodies you shouldn't use it. Also? Nail polish remover with acetone doesn't work very well. If you get acetone for removing paint, get the 100% acetone that is in the nail section of any walmart or pharmacy. It's pretty cheap.
2. Q-tips are your best friend. You can correct mistakes in an almost precision manner removing paint with q-tips, plus they get in places it's hard to otherwise.
3. I wouldn't attempt rehairing unless you've got a lot of time on your hands. Even if you just use a rehairing tool [you have to be careful to get a fairly small needle size as you can rip out the plugs of the outer hair line very easily as they are so close together], it takes at least an hour or two..Some times more if you don't have much experience. Needle and thread is also a very time consuming method. Honestly I've gotten to where if I'm selling a custom [or if it's for myself] I rewig them whenever possible. Most 5-6 size doll wigs, or pukifee and lati yellow doll wigs fit them. Monique size 5-6 wigs usually fit too. If you do decide to rehair, I've found that on average, for medium length hair you need two hanks [you quarter it instead of cutting it in half], and for long hair you need at least three hanks of hair]
4. Don't be too hard on yourself if you make mistakes. It's a learning process, sometimes it happens to everyone.
5. I use testors dullcoat spray sealant before and after [and in between when doing something with layers of pastels or paint] working on a doll face. It gives the paint something to cling to, and seals it afterwords. I use delta creativity gloss exterior/interior varnish to make the eyes and lips glossy.
6. The body doesn't hold paint as well as the face. Since they are different kinds of plastic, not only is the body prone to melting or slight disfigurement with acetone [especially if you aren't familiar with acetone], but paint rubs off very easily even when sealed before and after, so handle with care, and I definately don't ever reccomend body painting of any kind when the doll is going to a child of any kind that's under fifteen.
Hope some of these help