The pot is huge with all those callers. Tough to do much.
After he check/calls the flop, it's easy to put him on a set or a flush draw. When he leads the turn, I think I flat call for pot control. If he's not on the FD he can't be 100% sure that you're not on something like [Kd] -- so if the 3rd flush card comes and he doesn't have the flush, he'll have a very tough time repping it. On the other hand, if he is on the FD then at $50 NL it's unlikely he'll bet the river if it misses. Which means that any solid bet by him on the river is a hand that beats your lousy pair. So after your flat call on the turn, whatever hits on the river (except a queen), you can check behind or fold to a strong bet.
On the flop, you always CB your big pairs, no matter how many opponents are in. Most of the time they'll all fold and you take it down. But slow down fast if you're called. It's tempting to put the other guy on the flush draw, because that's the only way you can be ahead and we all like to be optimistic. But it seems like at $50 NL the number of set-it-or-forget-it players is way higher than the number of suited connector chasers or other tricky types.
I hate these situations. Very tough.