If your getting briefs and not competing you could probably get two sizes up from what the recommended size is and be fine. I would stay away from Inzer because their sizing has to be the most frustrating thing is the world and I have found with some of their stuff that you can order three of the exact same thing and only one will actually fit. I personally have had much better luck with Titan gear,their Centurion Boxer Briefs are what I currently use and I love them. By ordering loose you shouldn't have any problems getting them on once you break them in and they will still give you good support.
As for liniment you can find this stuff at walgreens called Iron Man Spray which is pretty mild but works good, or you can man up and get a tube of capsicum which will definitely heat everything up nice.
Finally if box squatting is easier on you then I think you'll be fine stick to primarily box squats, just make sure to throw in a little extra quad work because your quad involvement will drop off a bit with the box.
I should have been more specific in my first post lol, I just read that you were more of a powerlifter so I automatically thought you would be more familiar with terms like briefs. Didn't mean to inquire about your personal underwear preferences lol.