Wow ! very nice work !!
I like the control by muscles, it remind me about the Thymio product but I think it is completely different.
For the prototype of arm with hand… I was to do the same thing… But you already did 
I was doing the part to fix the first XL-320 to plug on the arm.
I see you use XL-320 to control hand but do you plug directly the first XL320 to the elbow servo mechanism ? Or is there another wire to control the hand ?
The book about convex optimisation is used in the video… did you read it ? 
Did you use convex optimisation to control the hand ?
For my artistic project, I will cut the hand to have 2 degrees of freedom at the wrist.