Make sure you get in good with the in-house sound guy!! He could potentially be a little resentful of some "no-name" guy coming in and jumping his gig for the headliner. If you can, just try to work together as a team to make the gig successful. If he's been there for a while (and actually knows what he's doing) he should have a pretty good idea of the system and the weird nuances of the venue.
Sometimes the headliner is the only act to get a sound check and then the openers just have to deal with it on the fly. Which means that even if you get to soundcheck your band, everything you tweaked in will most likely get jacked up before it's even your turn to mix. Therefore, if you and the house guy work together, you won't be jumping into a mix you don't even recognize.
Hopefully they will have a dedicated 1/3 octave graphic EQ for each monitor mix, and as has been mentioned before, take some time to "ring out" each monitor mix for feedback frequencies. Start with the singers mix and do a thorough job ringing it out. If you get that one stable then just match up all the other EQ's and you should be good to go.
If you are forced to use the console strip EQ for monitor EQ, and you have enough channels to do it, you could actually split your vocals into two channels on the board. Use one channel for the house mix, and use the second channel just to send to the monitors. That way you have some independant EQ for House and Mons. If you're trying to do feedback suppression on just one channel, A) it'll be a pain in the ass, and B) the EQ settings for mons will probably make the vox sound like ass in your house mix.
I've been doing live sound for about 12 years, both FOH and MONS, so I know that these things should help you out.