I have the problem of the biceps falling as well. I wrap them and put the biceps over the cuff of the vest. Then I added a snap to hold the bicep to the vest. That puppy dosent go anywhere. My shoulder armor is the same way, snap to the strap on the chest, and then to the vest. I dont do jumping jacks or anything.
The arm plates are more like lower elbow gaurds. I might ride mine a little high.
I also agree on the shoulders, adding a little to them would look better. The gap will look less with your biceps up. Just add a little to the bells...
great job bud. Not many build there own. I am totaly impressed!