So this guy already overbet the pot (~200)? Was he who made the flop bet? If yes you can rule out him having a flush.
How deep is your stack? If you guys are deep enough, a raise to ~650 sounds good.
Then call a reasonable reraise (if he gets the flush blame variance ), and fold to a huge push.

This is a difficult situation, which it usually is when you have 5 people limping in pre-flop. I rarely enter a pot without raising, otherwise it's too hard to read what you're up against.

My guess would be that he holds one of these hands;

2,2
5,5
A,T
T,J
9h,Th (or similar)

You are beating most of these, which suggests you should raise. If I had to choose a hand to put him on, I'd say 2,2 or 55. Might explain why he min-bet the flop, trying to fatten the pot, and then checked the turn hoping to re-raise someone with an ace, and then over-bet the river in desperation hoping to get some value for his set.