Sorry that I'm not giving real advice, I myself would need advice, too.
There is another first gig topic here, where I read quite a few good things.

I had my "first" gig last Saturday (I had lots of gigs in the late seventies, but then I stopped and had a 25 years' break), and I was really stressed and ill before it; I tried my best to prepare for it, and I had quite similar questions to yours, but when I went there and everything got set up in the last few minutes before the show, I found nothing arranged the way that I would have liked it. I couldn't even position my cymbals right, as there were cables and mikes all around, etc. etc. The show still went off amazingly well.
So as I see, don't prepare and expect too much: it's always on the spot and in the last minute that you have to solve your problems - anyway, anyhow.

+1 on what the nut said.   

And add to that, relish the hour and a half setup/check time.  That's luxury time right there. 

Check out this thread that I started last week. There's some great advice in replies there.

Basically, be as prepared as you can. As Drum4JC said in that thread, make sure sound from amps and stuff (if they're not through the PA) passes you so you can hear it clearly. Take advantage of the 1 1/2 hours you have to sound check (last week we had the same amount of time to soundcheck 9 bands - suffice to say we didn't get any sort of sound check at all).

If you haven't got a few backup parts, especially a snare, make friends with one of the other two drummers before the show and ask if you can use their spare in the offchance that one of your heads break or something like that. And of course say you will return the favour for them if they need to use anything of your equipment.

But most, importantly, of all, ENJOY IT! The first gig is great - the feeling on stage is fantastic...as you'll see.

Remember, if you happen to screw up, chances are no one in the audience is going to notice. Don't become pre-occupied with any mistakes you may have made, just forget them and carry on giving it your all!

Good luck.

I used to be a guitarist/vocalist in a death metal band so I expected my first gig as a drummer to be boring as sitting at the back on my own without being able to thrash out didn't appeal to me. However, I sat behind that kit and thought '@$%# it'. So I blasted my way through the set and just went for it. Charisma is so important. Really.

I split my finger on my snare drum, got blood everywhere but carried on and the audience went crazy to see me really @$%# it up. I then finished a song by headbutting my crash cymbal and now, everyone is still bringing it up in conversation. Just do what you do, be yourself and really put everything you've got into it.

Hey everyone,
The gig was last night and came off better than i imagined it would! Sound wasnt that bad and i ended up having my own monitor so all was good in that department.
I got heaps of positive comments about my playing from the other drummers and people in the crowd. One guy even gave me a cuban cigar haha. And i managed to pull off the drum solo without any noticeable mistakes which was great!
The whole thing was perfect and the atmosphere was so cool! 
Cant wait for the next one, which im sure wont be far away because we recieved a few offers to open with some other bands in the near future.

Cheers
Phil

Congratulations!  It only gets better.  Playing out is cooler than the center seed in a cucumber.