Wow, I'm absolutely blown away by the amount of knowledge in this post. I'd like to thank everyone who replied; it has truly been helpful. To some degree even eye-opening. I'm going to contact the instructor and come up with a plan now that I am armed with much more knowledge than I had. I'll circle back and reply with my outcome so that others can benefit if they run into a similar situation.
For those that were asking:
Yes, I have gone through physical therapy for my shoulder. I'm pretty maxed out on how good it will get without surgery. Trying to put off that surgery as long as possible as the recovery time is absurdly long and I've gotten past the 'living with pain' part and now only dealing with limited mobility reaching back. If this ends up being a limiting factor to what I want to accomplish, maybe I'll have to commit to getting it repaired.
In terms of gas I'm used to carrying .. I will adjust gas according to the dive and what my buddies are running. On a shorter shallower dive I'll bring either 2x40's or 2x50's. On longer dives I'll bring 2x80's (I don't like the feel of 2x100s. In order to get good trim they pull on my lower back in a way that's uncomfortable after 30min or so).
