Normal folks like millers or soldiers should be Might 2. NPCs that are adventurers–warriors, magicians, rangers, burglars, etc.–should be Might 3. If they have access to a spell, prayer or potion, they can use that to get a higher Might. You are, of course, free to increase Might as you see fit if it makes sense: they’ve just completed some crazy blood magic ritual, for instance.
I give NPC magicians and cultists spells and prayers out of the book. But I can totally see a case for just giving them spells as weapons in the conflict modes. It really just comes down to what you’re comfortable with as the GM.