Bet into the PFR or check raise the field?

[Vern]

Preface: I don't think I check/raise enough so I am looking to places to do it.

Table is nice and loose.

CO has obviously just sat down.
UTG+1 is loose and passive before and after the flop
MP1 is tight and aggressive preflop, tight but not as aggressive post flop.
MP2 is loose and passive before and after the flop
BB looks tight and passive, only one orbit but nothing crazy.

Party Poker 0.5/1 Hold'em (9 handed)
Props to Bison for his converter

Preflop: Hero is MP3 with 5[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/club.gif[/img]. CO posts a blind of $0.5.
<font color="#666666">1 fold</font>, UTG+1 calls, MP1 calls, MP2 calls, Hero calls, <font color="#CC3333">CO (poster) raises</font>, <font color="#666666">2 folds</font>, BB calls, UTG+1 calls, MP1 calls, MP2 calls, Hero calls.

Flop: (12.50 SB) 5[img]/images/graemlins/diamond.gif[/img], 6[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(6 players)</font>
BB checks, UTG+1 checks, MP1 checks, MP2 checks, Hero ?

If I bet and CO raises, there will still be 15.5sb in the pot, with people calling 2, they are getting 7.75:1 and I doubt many will fold. I think there is a better chance CO will bet if checked too than raise if I bet into him. If they are likely to call two anyway, I want them to call two and check raise this field here? I think if he bets at least 2 others will call. I am about 2.25:1 to fill up or 4OAK by the river. Is this a good spot to check raise or am I moving towards FPSitis? Should I want people to fold incorrectly (when they had odds to call) since the pot is already getting big? Also, I cannot three-bet him if he raises me and check/raising may shut CO down. I am very confused.

Vern

Standard Disclaimer, I am by no means an expert at any of this.