Others have sufficiently addressed the "contradictions" part of your post so I wont go there.A couple more: Collar or harness? Short leash or "spring loaded extendable?"
Finally - and off topic - this dog loves learning tricks. He catches on quick, and has excellent memory (so far). One thing he hates, though - ROLL OVER. He loves to do it on his own, he loves belly rubs, but he will not do it on command...?
Depends on how strong your dog is and how well you have trained him to walk on a loose leash. If he is constantly pulling your shoulder out of your socket, I would be fitting him with a Gentle Walker Harness and using a strong leash and actively training him to be more polite and walk with a loose leash.
If he walks politely and has a good recall, then a Gentle Leader Halter with extendable line would not be an issue.
On the roll over, go back to basics and shape it. Nice tasty rewards given for each step towards the final action. If he continues to be stubborn, when you have him lying on his side, with his head up and back looking over his shoulder, you can always grab a hold of the front leg thats on the ground and use it as lever to flip him over - huge rewards when he goes over.