I have a stock Glock 17 right now I have 2 belt mounted magazine carriers could be more if needed.
First what is the best class for a noob? I am thinking limited but not sure if that's the best choice?
As Fly said, "best" is really relative. (And it is "division" not class, just to get you used to the terminology. "Class" means something else in USPSA.
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I'd suggest either Production or Limited (shooting Minor) for your first match. Doesn't mean you have to stay in that division, but either would be perfectly fine.
As was said, in Production you are limited to only 10 rounds in a mag after the start signal. As such, most Production shooters carry
at least four mags in pouches in addition to the mag that starts in their gun. (Some, like me, carry more.)
If you shot Limited Minor, you could run every stage with only 3 magazines, because you could load them up completely. For your first match, that might be an idea, simply because while you'd still have to reload on the clock, you wouldn't have to do it SO OFTEN, and so you could spend more of your time thinking about shooting and safely navigating the course of fire. Once you got used to it, switching over to Production could happen.
Second questions how many mags do I need on me during a stage on avg? I know mag capacity limits and stage design affect this answer but can we say on avg?
Max round count per stage is 32. (Well, technically it could be more, but in general, you won't see any over 32.) As such--in Limited, most people run the stage with two mags. In Production, normally 4.
No matter what, you generally want sufficient mag pouches to hold all mags.
Seriously, for most people a good place to start is Limited Minor. Less restrictions on holster type and placement, less need for extra magazines and pouches plus fewer restrictions on placement, and you can load up your magazines.
After a match (or two, or more---maybe you'll like Limited!) then you can think about what division most closely matches your equipment, and how you want to shoot matches.
....I see that Mud has already written about this too, so you don't really need me saying the same thing again, but since I've already typed it, I'll post it.
