Agamon
Adventurer
Belts of X Giant Strength are pretty iconic, I think it's a fairly safe assumption that they'll exist in 5E.
I'd bet the farm against that.
Nope, it's permanent. At 20 Barbarians get +4 to Str and Con and their new maximum for those is 24.
Ah, well, that's not so bad. L20 = end of campaign (assuming one ever gets there). It's okay to break the game for the final climactic BBEG fight.