“What I’m having trouble with is the rotator cuff of my string arm. In order to ensure full expansion, I pull back until I feel an intense stretch in my rotator cuff. I’m pretty sure this is overdoing it, but to what extent should I expand?”
There is a “slot” through which your elbow can go comfortably while making a shot. If your elbow is too high or two low, there can be a feeling of something “catching” … which is bad. How high or low your slot is depends on you. I have seen archers with quite high and quite low arm positions/slots.
You need to find your slot. With your lighter limbs on your bow try drawing (you don’t have to shoot) with your elbow way too high … then way too low. Focus in on the feeling in your draw/string shoulder. Then try draws at various other spots. Being of a systematic mind, I would go half way between “too high” and “too low” and then look to slots in the top or bottom half of that range depending on which seemed the most promising. So, eyes closed, focus on your shoulder, draw. Try different arm slots to see if you can find the one that works for you. It should be comfortable with no strain and no pain.
This is something I learned “along the way,” I don’t have any biomechanics to back this up. Let me know if you do.
Also, take it easy. You are still nursing an injury which you do not need to aggravate.