How many servo motors should I be using?
Hey- glad you're making some progress!
I didn't read those hand instructions in any detail, but it seemed to me there's a string in each finger, is that right? Then I suppose at a maximum you would need a servo per finger. On the other hand (sorry about the pun), maybe you could gather the strings together and activate them with only one servo. Or somewhere in between- space and weight will be a consideration. You will need to experiment with that- that's part of the fun of this whole thing. I think too, that you'll need to experiment with servo positioning relative to the hand, to give the right angle when the strings are pulled, and build some kind of base for the whole thing.
Then you'll need to figure out how to attach the hand to the arm- the arm I showed has three servos: 2x standard size a "shoulder" in a pan / tilt bracket
and 1x micro as an "elbow". Number of motors depends on the number of joints and the range of motions you need.
As an aside, I've asked my local supplier to see if he can source a pan / tilt bracket like that for micro servos: it would make a cool wrist.