The rule system is GURPS 4th Edition. The books that I am culling from include Characters, Campaigns, Powers, and Martial Arts. It’s not necessary for you to go buy all the books, but I do recommend that you at least get familiar with the basic mechanics of GURPS. You can always get a free copy of GURPS Lite from Steve Jackson Games, which contains most of what you need to know. I have to approve all characters and will work on them with you anyway, so you can even just talk about the character you want with me and let me design it. As far as how detailed we will get with the rules, I’m trying to allow as much granularity as I can while keeping everything moving at a good clip. A three hour session to run an 8 second skirmish is unthinkable to me.
Aside from this, don’t be a jerk, try to show up on time and stay for the session, and make the session fun for everyone, which is the whole point.