This is a very complex task which you are trying to carry out but has the potential to be something amazing. I presume you want to try to replicate the human hand as best as possible however I suggest you simplify your design for your first attempt to minimize the complexity.
I would simplify as follows:
1. Treat the palm as a solid platform, a human hand can curve in the middle but for starters it would be easier remove this motion.
2. Each finger has 2 rotational DOF's where they meet the hand, to simplify this fix one of these DOF's on each digit (including the thumb) so that the hand can make a fist.
3. You should now have a hand with hinged joints only, to control these I suggest you use a cable mechanism with a rack and pinion to control them. This should give you some degree of accuracy.
Does that help at all?