theres a ton of stuff in here, but thats not whats gonna be going through your head. Heres the stuff that really gets at us....fear. "what if they make fun of us, what if no one is there, I suck, we suck, this sucks, I cant hear anything right like it sounds at home, etc etc etc.
So, Dont let the fear get a hold of you....Dont get high or drink to quiet the fear down.... Its natural, its part of gigging. Gilmore says he still gets scared to go on stage...
Yes it will sound different than at home....Drummers never can hear anything in their monitor, its usually blown...The singer will sound like hes singing through an AM radio in a 76 ford pinto.....Your guitarist will sound like a dying cat in a garbage can and your bass will sound like a tuner car at a ghetto car stereo meet with 24" subs.......who cares.
......practice at home before the gig set up in different places and have everyone play at different volumes than normal....it will still sound awkward to the point of you will have to force yourself to play the first few songs....
Its harder to play for 5 of your friends and family than it is for 5000 people you dont know....you get a lump in your throat and you know you have to talk to them after the show....you will be fine. Practice, practice and practice some more so you can play on autopilot.....who cares if you suck, be a well rehearsed band that sucks, you will sound better.
Keep your mouth shut and your ears open, be nice, be real, courteous. Hell, tell the soundman youre nervous and its your first gig, he may well help you out.
All in all, might suck, youll be terrified, the crowd could be horrible, a huge labor effort and crappy pay, but just for a moment, you will be on stage, you will feel great and you will realize that you are a musician for a reason, this is what youre designed to do, and everything is right with the world for that minute.....you will be so stoked that you cant wait for the next gig.
enjoy.
Oh yeah....dont forget your amp at home.....