Max will be Int score for that, Jaron. I take it you've used NSRCG before? Are you familiar with creating with the Karma system? (I've played both of those, by the way. Hell, my cat shaman was a former assassin.
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Reminds me. You'll be creating characters on 425 points with a max of 1mil nuyen - aka, the defaults on the Karma system. (Yes, that's a lot of money. It goes very. Very. VERY fast.) Warning for when you get to Edges and Flaws. Although the listed values are 1, 2, etc, each one is worth 5 times that in Karma (5, 10, 15, etc.) You'll get up to 6/30 points of Edges, and no more than 5/25 of flaws.
NO otaku allowed. I'm sorry if anyone thinks they're neat (although it seems no one's had a problem with that yet, but I had forgotten about them.) And no Surge characters. (You'll find Surge stuff in the Edges and Flaws... don't take any of it. Anything that starts off with SRG, in other words.) No ghouls as well, and I'd highly recommend against shapeshifters.
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Generic, nothing stops a mage from having a gun. What does make a difference is that mages will usually have their best skills being their spellcasting, and a cybered character often has several bits of 'ware to help with that shot - in short, cybered characters tend to be much better at shooting than mages. (This is not necessarily so - just often the case. One of my old characters was a physical adept who specialized in being a sniper, while I had a mage who was a crack pistol shot.)