Flopped straight on all diamond board

[Hofzinser]

It's a live £10 (approx $20) rebuy tourney.

Down to the final 25 or so players. The blinds are at 350/700 (rising every 20 minutes), and I have approx 13,000 chips.

I'm sitting in the BB, and a guy (approx 7,000 stack) who had been playing pretty loosey-goosey opened with a raise to 2000, 2 off the button. The button thought for a bit and then called (his stack was approx 14,000). In the BB, I decide to take a flop for an extra 1300 with 4c 5c. (Loose, I know, and most probably flat out wrong, but let's ignore that for now.) So there's 6350 in the pot.

The flop comes Ad 2d 3d

I'm first to act. What should I do?