It depends a lot on what you intend for the end result. If your animation is going to look more full (less like a puppet) then you should really segment them at the joints (shoulder, elbow, wrist) and either weight the joints (shoulder to arm, arm to forearm, forearm to hand) or segment them at the joints like previous example and place patches beneath the elbow and hand joint so that the wrists and elbows have freedom when swapping image attachments.
You're more likely to regret trying to making something as versatile as a more realistic arm as a single piece than to use a combination of objects that can be re-weighted super fast. Especially when you start re-introducing objects or need to reset your weights.
My experience for the past few months have been: rig it as though you'll have to re-weight each object 3 times. If one weighting will take as much time to do once as having a separate piece - then break it down farther. Resetting weights and meshes are common as you find you want different motions, so you should spend as little time applying highly particular weights as possible. For parts that are more fleshy like the shoulder, you can use extra bones set to IK in order to hold a better silhouette. See the tree hierarchy here to see how I set this one up.
Weight the inner armpit to follow the bone and weight the outer shoulder bones to defer more to the IK-bound bones. Find a blend you like - for this example, all I did was auto-rig, hit smooth, and left it as is. It could use work but it functions. With this kind of rig, you can also animate the IK_Target as well as the translation of the first controller bone. I've gotten very nice effects with an almost full range of motion using this on shoulders, biceps, hip shapes and calf muscles. However things like forearms which rotate with the hands, you'll want to switch between images and so don't want them bound to an entire arm rig.
This can be greatly improved with additional weighting and vertex placement fixes- but this is a result you can get with no adjustments to the mesh other than auto and smooth (on the shoulder)
GOOD LUCK!
