This photo tutorial is a step by step WIP for making an armature for a hand and how to add clay over the wire. http://www.renatajansen.co.uk/gallery/tutorials/hand_tutorial.asp
For larger dolls, you may want to try using an armature like this as you can get stronger fingers and lots of detail. Some doll makers use them in smaller scale dolls too. Try it to see if it will work for you.