[DCJ311]

The fact that the Ah is on the board makes it seem less likely that your opponent's hand actually contains an Ace, as most players would not check this flop with the flush draw on the board, although it is very possible. Therefore it is not imperative that you bet here, because if you lead out 20-25k you will get raised all in by a guy with Ax, and you definitely are in a bad position if this happens. If he does have an Ace, and you hit your flush on the turn, you may be able to extract some money out of the hand, or get him to make a delayed continuation bet bluff, where you can raise HIM all in or call behind and see what happens on the river.

If a K or T comes on the turn after you check behind, and he checks to you, I'd probably check again. If the turn comes blank like pairs up or comes low, you should probably lead out something here, since you now want to pick up the pot with a 20-25k as if you get c/r allin, it's not as big a disaster as it would have been on the flop. If the turn comes Q or J I'd probably check behind again, and auto-bet the river if he checks again.

This is definitely a tricky hand to play b/c of stack sizes, but I'd be hesitant to bet that flop because you don't want to get blown off the hand and there's not a lot of value in betting there (unless your stack size were like 70k in which you could just shove it all in) when potentially you could create a big pot on the turn or bluff it on the turn yourself, where it looks more like you slowplayed.