1. 

I think the mininum number of cables required for a robot hand to move is at 2 cables, I think thi* *ecause you would need one cable for the arm, and one cable for the hand. For better results tho, you should use even more cables like 5-6 for the fingers and more DOF in the arm and hand as well.  I think 2 cables would work one for each of the tendon's. 3 and 4 cables would allow the robot arm to work even better by providing more DOF's to the hand. The more cables the better, as more DOF up to one point.

2.

I would design the arm part to look almost identical to a human arm same amount of nerves, tendones, muscles, and more. I would use at least 8 cables to be like the 8 tendonds in our hands.

3.

I would do the same thing with the hand part of the robot except that ill have a cable for each of the finger's and probaly 2-3 more for extra movement. So in total about 8 again.

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