1st and foremost - raise PF with AT. Its not that you have a great hand, but you want to make sure hands like this don't control the pot on you. From his point of view, he is 2 from the button, and no one has done anything but limp. Even just min-raising the PF, he's taking control with a weak hand.
Flop - you're right, if he's going to raise your bet here, you're not getting him off this hand. if you feel he's drawing, push to gain odds
. If you're not sure, flat call is okay.
Turn - his betting so far has all the hallmarks of a low flush. minraise PF for control, minraise flop on the draw, all-in on the 3rd spade. In any other game, I would say fold and kick yourself.
Here, though, you may have to call just because of all the donk players at this level - from what evryone keeps telling me, half the players are gamblers and not poker players, so you should call but not be suprised.