I continue to learn this game (mostly i play NL), and this hand was a bit weird.

I got OTB, 4 limpers, I raise pot, and get called by 4 people.
I have full stack, all the callers have full stack or cover me.

Flop (pot 11):
SB bets pot, one fold, 2 calls,
(pot now is 55) basically if I raise AI here it will be 4 way AI (I doubt that anyone would fold), should I fold or go AI?

I suppose that I am beat right now by set or straight, though I have a nut flush draw and there is so much money in the pot.

Just call. Why do you have to push all in or fold? This isn't holdem, you don't win an extra special kiss on the bell-end from the dealer for being the most aggressive player on the table.

I suppose actually having re-read it, there's not that much $ left so you will probably lose a coupla calls if the spade comes on the turn so yeah pushing seems fine. My one worry was that you'd lose a call (or two) and thus your flush draw would be worth less. FYI, you probably hold somewhere in the 25-30% equity range (depending on what other hands are out and assuming there's at least one set there, which might not be the case). Also as Brian says if the board pairs and there's action to you you're probably drawing to 2 outs....

Any case, you're not folding.