So I had an idea for a setup I'd like to run at some point in the future. It'd be nice to have an experienced mod look it over with me sometime and see if it's balanced. Obviously I'll need more experience playing before I try to mod a game, but is there any guideline for how many games sometime should play before they become a mod?
I don't think experience playing is really important, what matters is experience modding. I think it's recommended that you co-mod a game with a more experienced mod first before modding a game yourself. Co-modding gives you a sense of what goes on behind the scenes without forcing you into any difficult situations. But really, I think as long as you're organized and dedicated enough (which I assume you are), then you should be fine jumping right into it.
I am always happy to look at set-ups since I don't plan on playing mafia again any time soon anyway, but there are probably other people who could give you better input.