Registered here just to chime in on this -- think what you are doing is amazing and you are helping me understand what it would take to do something like this (not ready to undertake but every bit of learning helps).
Also wanted to say - in your idea of how the suit fits together (shoulders straight, elbows for shoulders and wrists for elbows) -- i went back and looked at the opening cinematic for Wings of Liberty when Tychus is being fitted into his suit and that's exactly how they designed it. Here are some screenshots:
You can see the joint here, plus a "control" that lets him use the "fingers" on the "glove" -- the wrist area has a joint that only pivots right-left (effectively making this the elbow of the suit). Kudos for figuring out how Blizzard intended to make this workable.
Hand in, grasped controls, plate coming down...
Plate going into locking position (there is a cage integral to the gauntlet)
This is a pic from behind the suit - as the "shoulder" is being fitted on - that yellow part is where the shoulder attaches to, and that would basically be the elbow (human anatomy. If you stare long enough (doesn't it look too long to be a human arm?) -- you can deduce that Tychus' shoulder is under the exhaust, and the elbow is inside the yellow cage, and the hand (pics above) has a joint to make the "elbow" of the suit).
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Hope this helps make this thing awesome

If you need more reference shots, i got these from the game Wings of Liberty - but you can go to youtube and search for Wings of Liberty opening cinematic (this whole thing is there in high def)