if i may suggest: when rigging the shoulders, make the collars scalable in the x-axis to facilitate moving the armpits outward just a bit when bending the arms down (via ERC)so the arms drape outside the ribcage... current fugures have no provision for this (and animating joint centers is a joke) i think collar X scale may be an answer... looking good  on the modeling so far, great attitude on suggestions, enthusiasm A+ ,you're getting there...

:O)

Y'all have a great day.