Nut flush on 4flush board. Bet sizing question.

[Jeff W]

10-20 6max

Villain is a weakish regular. 28/13/1.5 overall.

Seat 6: Villain ( $3789.50 )
Seat 5: Hero ( $3414.50 )

SB posts small blind [$10].
BB post big blind [$20].

** Dealing down cards **
Dealt to Hero [ Ks 8s ]
Hero raises [$70].
Villain calls [$70].
SB folds.
BB calls [$50].

** Dealing Flop ** [ Qh, 6s, 7s ]
BB checks.
Hero bets [$150].
Villain raises [$400].
BB folds.
Hero calls [$250].

** Dealing Turn ** [ 9s ]

Hero bets [$750].
Villain calls [$750].

** Dealing River ** [ As ]

How much should I bet?