In New Hampshire there are no requirements. Though the WMNF as well as your outfitter insurance company may not be so content with the minimums.
If guiding rock or ice I'd suggest you work with the AMGA as it's a recognized route. If guiding hiking, I'd stick to the sort of route I went:
I earned my AMC Class 1 Leader badge, plus I guided with some good meetup groups like Random and NE Peakbaggers (all for experience), took outdoor leadership school, took the AMGA SPI anyway, took Avy 1, earned my WFR and with CPR/AED have kept both current, became an LNT Awareness Trainer, studied my ass off, volunteered with SAR to further test myself and put myself into situation I could learn in, plus I have partaken in F&G training opportunities afforded by said volunteerism.
Depending on what you're doing out there will affect what you truly need. Do plan to be far more prepared on every level than anyone you lead. Physically, mentally, judgement, gear, etc. In any case, it's pretty serious if you're guiding above treeline, especially in the winter.
A good way to start is to apply to an existing agency. If you get in, you're in. Climb on from there.
If looking to guide rock and ice, I'd suggest contacting Brad White at
IMCS. If looking into guiding hikes, I'll talk to you.
Apply here.