A second bubble hand question

Has to be from memory.

$11 Party SNG
Blinds 25/50
4 handed
UTG has ~t2000, Button ~t1000, SB(Me): ~t1000, BB: ~t4000

For the past 5-6 hands, BB has bet 500 chips to steal the blinds/limps if no one has raised before him.

I'm dealt K3s, and limp in. BB raises to 500.

Now, I figure he's doing this with any hand, so I'm guessing I'm ahead, but probably not by much. Is the correct play to fold and wait for a better opportunity? I went all in, assuming he'd probably fold, and if he didn't I had better than even money to double up. [Edit: new question] If I shouldn't push here, what range of hands do you push with?

Second question: he called, and turned over 104. Is this a good call here? He's got to assume he's behind, probably to 2 over cards (turns out he wasn't, but he didn't know that). If he folds, he's still got a 1500 chip lead on 2nd place, and a 2000 chip lead on third. If he calls and loses (likely), he's only got a 1000 chip lead on two players. Plus, keeping the bubble alive as the chip leader seems like a good thing anyway. I know I'd fold 104 here - is that the right play?

Thanks for any help.