for using your carry gun! Nothing against the guys with competition rigs and vests, I prefer to carry what I'm shooting and shoot what I'm carrying. I only use 1 spare mag when shooting the glock because I never carry 2 mags with it, too heavy. Most clubs will let you shoot whatever you want to get you into game, they are kind to the new guys and very helpful.With a 6+1 gun I'd definitely bring four mags. Use 2 on the weak side 1 in the gun and have one to top off your chamber without having to thumb another round into the mag on the firing line. If you don't have mag pouches/dont use them, just throw your spares in your pocket. IDPA should teach you how to improve your carry habits as well as your marksmanship and performance under stress/on the clock. It also teaches you a lot about the gun you are carrying/ how to clear malfunctions quickly. It's a blast too.
I've been to the Arms room and Shiloh matches. Both are top notch groups of guys and great facilities and courses. Have fun!