Pushing vs. pot-committing with 2 pair

[parttimepro]

5th hand of a 109 STT at Party. I get JTo in the SB. 2 limpers in early and middle position. I complete and BB checks.

Pot is 60. Flop is QJ3 rainbow. I check, BB checks, EP bets 30. MP calls, I call, BB folds.

Pot is now 150. Turn is T, completing the rainbow. I check, EP thinks for a while and bets 75. MP calls. I raise to 500. This is my first question: should I have bet more to eliminate any tough river decisions, or is anyone who calls this basically pot-committed?
EP folds and MP calls.

So the pot is now 1375. River is an A, putting the four-straight on the board. I think for a while, and decide that I'm not going to fold if MP pushes. He'll push with a K, of course, but might check behind with a worse hand. So I push. Second question: should I have just check/folded here? Isn't an A about the worst possible card for me? It's really hard to think of hands he would have called down with that I beat now. AQ, KQ, KX all beat me now. Only something like Q9, Q3 are behind, and those aren't very likely.