Not true. Bodybuilders keep eating a lot to maintain their mass even when they reach their goal, otherwise they'll lose muscle.
I don't know. I find it hard to believe that no one would seize this opportunity to try and take him out and usurp him. I mean, have you seen the way he treats his henchmen?
If I remember correctly, there was a flashback of Bane after he got beat up lying on the ground. Now, I know I can't PROVE that he couldn't stand up, but I believe it's strongly suggested.
As for him fighting with a broken mask, that was only with the first tube broken, so it's not like his pain killers were cut off completely yet. And lol at breaking the pillar. That was another moment that bothered me. Trying to ground a comic book movie in reality yet giving a man with supposedly no super powers herculean strength.