KK flop K but also a nut flush draw

[TheStandman]

Did I play this good preflop? And what should I do on the flop?

(I don't have a good hand converter but I hope this is clear...)

Seat 5 is the button
Total number of players : 5
Seat 1: S1 ( $16471 )
Seat 3: S3 ( $5000 )
Seat 2: S2 ( $17376 )
Seat 9: S9 ( $5525 )
Seat 5: S5 ( $7060 )
S9 posts small blind [$25].
S1 posts big blind [$50].
** Dealing down cards **
Dealt to S2 [ Kc Ks ]
S2 raises [$200]
S3 folds
S5 folds
S9 folds
S1 raises [$625]
S2 raises [$1300]
S1 calls [$825]
** Dealing Flop ** [ As, Ts, Qs ]
S1 checks