A-5 Triple draw beginner's question

I just started playing A-5 triple draw and I have a basic question about playing on the button. I was dealt A257K on the button. Everyone limped, so there were 5 players in the pot. I have the following questions:
1) Should I have raised? (I didn't raise)
2) Everyone drew 2 cards. I tossed the 7 and the K. Should I have kept the 7 and drew to the 7 low or was I right to toss it? I figured that the 7 wouldn't have held up in a multi-player pot even if I did hit it.
3) The second round went Bet, call, call, call and I folded because I blanked. Was my fold here correct? I've been operating under the assumption that I need to improve on every draw. So far, I've been playing hands that I can draw 2 to a 5 or 6 low and if I don't improve I'll fold on the following round. But sometimes I get tempted to call on without improving. Like in this case, I'm drawing 2 to a 5, but there was a lot in the pot and it looked like a lot more would come, plus I've got position. So maybe in this spot I should have called? I'm a BEGINNER, so go easy if my thinking is not correct. I don't really know what I'm talking about....