My upper arms have been shimmed in the back and a snap has been added to attach them to the shoulder. One of the main sources of pinching in the costume is between the upper arms and forearm. Keeping the upper arms high on your arm keeps this from happening.
The forearms I simple riveted together. It really depends on whether or not your hands will fit. I wound up having to shim my right arm. Both forearms have extensive trimming and heat bending to keep them from pinching the inner elbow and wrist.
The hand plates have a small piece of elastic glued at the front for my middle finger and a velcroed loop at the back that goes over my palm. Eventually I may glue the loop at the back of the plate and go over my wrist. For gloves I use a pair of leather gloves I found at a flea market. They're not great since they don't go far enough back on my wrist and wind up getting pushed forward by the forearm pieces but the leather is good for grip. I used lycra gloves for a while and could not adjust my armor at all since my fingers would just slip off the plastic. I've heard people have had good luck with nomex flight gloves and batting gloves.