Good luck with the surgery. I know a couple of people who've gone through it. One is in her 80s and started shooting skeet again about a year after the surgery.
Start practicing the one hand shooting now. It's a good idea anyway. Never know when you might become incapacitated if ever in a...
I've got 3 Lee Pro1000s on my reloading bench. Despite their less that stellar reputation, they have served me well for many years. I like being able to switch between calibers without having to change anything over. And I like being able to keep a relatively few replacement parts on hand...
I have a hard time understanding why any of the cos who value their 2A rights wouldn't maintain a pistol permit as a backup. One is none, two is one, and all of that.
Might depend on the upper, but if it says it works on mil-spec, you would be good to go.
None of the gas system is in the lower. It's all self contained in the upper.