PokerStars (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Seat 1: nuclearbrobb (3244 in chips)
Seat 2: JerzyCat (4486 in chips)
Seat 3: Hoggen (5587 in chips)
Seat 4: Allison (1170 in chips)
Seat 5: snoshu (4299 in chips)
Seat 6: Gemini Ox (1500 in chips)
Seat 7: ace6pays (1887 in chips)
Seat 8: gumbajo (2060 in chips)
Seat 9: Hero (6180 in chips)

Blinds are 50/100

Preflop: Hero is CO with 2, 8, 4, A. SB posts a blind of 50.
2 folds, MP1 calls, MP2 calls, 1 fold, Hero calls, 1 fold, SB (poster) completes, BB checks. (Pot = 500)

Flop: K, 5, 7 (5 players)
SB bets 100, BB folds, MP1 calls, MP2 folds, Hero ???

so that's probably the best possible flop i could get, but what do I do? I think it would certainly be the wrong choice to slowplay it, but how much should I bet to not scare everyone away?

PS: I know I maybe should consider raising preflop, but the pf play is horrible, and I don't wanna loose big to something like A38Q suited...

I put in the raise here because another A2 is not going to fold. Make him pay to draw at 1/4 of the pot and win a big pot if he doesn't hit, and still a nice pot even if he takes 1/4 of it. I don't think there is any other play here except to raise.

After re-reading your post I am going to guess you are playing PL O8 even though I don't see that anywhere since you asked how much to raise to. I make it about 350-400. You really don't want to lose either player here but you want to extract maximum value.

oh yeah, you're right, sorry...it is PL O8

if you're not going to pot this preflop then what are you going to pot? you have a big stack you should be attacking those limpers.