There are two sort of ideas that come to mind. The first thing is if you want independent layers (which I think you do), then the nesting heirarchy is now important. You attach things to your parent. Here is what I did to your PSD file. Notice the hand is inside the forearm, which is inside the biceps. The ordering is important for depth of the layers. But doing this allows me to attach each layer to its parent.
Here is the rigging. Note that the origin (dotted circle) I dragged over the parent layer so it turned green and attached.
The "forehand" then joins to its parent, the biceps. etc.
The next question is the attach properties, where you have to options. You can use "hinge" or "weld" (or "free" if you are into dismemberment! You can drag the arm away from what it is "joined" to which is "interesting" - sort of like one of those hover drones sticking to where your hand is, but separate). I found with "weld" the sticks were important if you want to keep straight arms. Just try the different hing vs weld to see what works best for you. Hinge I think is the closest to what I think you are trying to do.
Oh, make sure "Attach To" is auto. You can try other values, but generally I find auto gives the least troubles. (I have only seen one case where "auto" was not the right answer, and I forgot what case that was its so rare!) So if its not "auto", change it!
Personally I normally do what Jerry says and not have independent arm segments, but that is up to the artwork and what is trying to be achieved.
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