I realize this is a very simplistic drawing, but it's very helpful.
I have used acrylics to my former dolls and as I saw its not really a good idea. Isnt there some colors that dries with a heatgun/hair dryer?
You could try using ground up pastels. You need to spray the doll with some kind of matte sealer like Mr. Super Clear or Testor's Matte before and after you apply the pastels.
You can pull the string through the joint with a bit of wire and some thin ribbon. try looking up doll stringing vids on youtube, that might give you a better idea. :3