Really good work. Hands and feet are the toughest thing to model for the reasons you are finding. In fact, even the face is easier because it is more elastic when you rig it with bones - stretching is ok. No advice really. Hand bones are and their influences simply require a ton of finessing. It's both frustrating and rewarding when I look up at the clock, four hours have gone by and everything I'm working on is better, but just by a little!