As a rule 1000rds is about it, give or take 200. Letting it cool is key. But if your not the one that put all the rounds down the barrel, then you'll never know, and the damage be already done.
As far as barrels go, any of the custom barrels you read on this site are top quality. There's a lot of them too:
Walther Lothar........are some of them.
What I will tell you is to first come up with a contour you want. Then check out all these makers and find one that is in stock( if any of them do) because sometimes there's a wait.
Can't help you too much on the muzzle brakes
, I don't run them. My 300WM has a Palma contour barrel and is heavy enough where I don't need one. Lots of great info on that subject in the search engine, on this site.