KQ against unknown

Finally decided to post a hand after lurking for a while, would appreciate any advice/criticism.
What gave me difficulty in this hand is that button only joined the table a couple of hands ago so I had no idea what kind of player he was.
Is it correct for me to call down once he capped the flop or should I fold?
Is the check preflop alright considering the amount of players who limped? I doubt my raise would make anyone fold.

Ultimate Bet 0.50/1 Hold'em (9 handed) converter

Preflop: Hero is BB with K[img]/images/graemlins/heart.gif[/img], Q[img]/images/graemlins/club.gif[/img].
<font color="#666666">1 fold</font>, UTG+1 calls, MP1 calls, MP2 calls, <font color="#666666">2 folds</font>, Button calls, SB completes, Hero checks.

Flop: (6 SB) K[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(6 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, UTG+1 folds, MP1 folds, MP2 folds, <font color="#CC3333">Button raises</font>, SB folds, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">Button caps</font>, Hero calls.

Turn: (7 BB) 7[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Button bets</font>, Hero calls.

River: (9 BB) 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, Button checks.

Final Pot: 9 BB

Thank you!