[DeuceKicker]

I'd raise to 600 preflop (assuming 3BB is considered a 'standard' raise in this tourney). This will usually buy the blinds and I'm OK with that

I think the flop bet is fine. You're giving draws 3:1 odds, which is not enough. 400 would be fine, too, I think.

The turn is where I usually wuss out. The flush draw hits and he bets such a small amount that I start out-thinking myself. "Is he trapping me, making a weak bluff, or trying to stop me from betting bigger so he can chase his draw?"

I'm not sure what the optimum play is (because I suck) but since he has you so out-chipped, I think I'd just call. Even if he hit the flush, the pot is laying you 5:1 to boat up, and there's a very good chance that you have the best hand. The obvious drawback is if he is looking for a 4th diamond, you're giving him great odds to draw.