First and foremost, congrats on the gig. We all gotta start somewhere, and I’m sure the manager will have a little listen at some stage during the night. They usually do anyway. 😉
Secondly, onto your setup. You’ve got it cracked already. When I played my first gig, I did it almost the exact same way. I’m using Ableton with an AKAI MPK Mini controller. The way I did it was to run a line out from the headphone jack, with a Y splitter, into the CH1 Input on the club’s mixer. The CH2 actually had my backup/emergency ipod in it, just incase of any disasters. In anycase, back to the laptop. In terms of levels etc, put and leave your laptop on a high volume, but not 100%. I find 80-90% works best on mine, but each laptop is a little different. Then have the levels on the relevent channel on the mixer, CH2 for example, on low, set a track playing, and bring the levels up slowly. You’ll then be able to get an idea of the various levels you can have your setup at throughout the night.
This brings me nicely onto a few little tips. Firstly, when you have that all done, go have a wander around the area to see how it feels. You can always adjust eq to get it sounding just right, particularly on things like bass and treble levels. I found that my setup sounds a little bassey before the gig, but usually sounds better when the room is fuller. Secondly, try to get an idea of a good low, medium, and loud setting on the mixer for your set. It’ll allow you to adjust the volume depending on the situation. Finally, keep an eye on the VU meter on the mixer. Remember, if it’s in the red, it sounds shit.
Hope that helps. I’m a bit of a novice DJ too, but that’s the best of my experience for you. We’re all total noobs at some stage or another, but you seem to have a good idea of how it’ll all work. I’d definitely recommend a sound check, particularly for your 1st gig. It’ll give you time to double check what you might need.
Oh, and a 3.5mm > 1/4′ jack adaptor for your headphones into the mixer. I forgot those at my 1st gig and had to get a friend to rush back home and lend me his lol!