I don't think this really makes sense... they're still just normal humans. It makes sense for dwarves, but not so much for just nomadic humans. You don't have to like or believe in magic for it to affect you. A fireball still burns you.
-Merenary wizards with the mercenary tech (merc wiz's should be cheap, get random spell promos, and perhaps have a turn duration)
Sure, though you should probably also give these units to Tilea (king of mercs) and they should probably have another tech requirement - maybe mercenary contracts and winds of magic, or mercenary contracts and literacy or education. Have them start with 2 random level 1 spell promotions (from the elemental or wind magics) and channeling 1.
-pretty decent Ulric and Taal priest UUs
Sure. Why don't you give them some beast and/or life magic spells?
-strong defender units, speedy heavy cavalry, relatively mobile army.
I think these are mostly fine in the existing army list. You could give one of their leaders the Horselord trait if you like.
-steal the tundra/snow affinity effect from the Illians in FfH (+2 food from snow)
I think Illian snow is going to be like hell terrain in some sense. Snow != tundra or ice (current terrain types). Besides, not even Kislev can really get any food in these areas.
You could give them +1 food from tundra pretty harmlessly, which would capture the flavor of what you're after.
-good defencive building UBs
Really? This feels out of flavor; slavic russians in wooden forts hardly have better defenses than dwarves or the empire building mighty stone fortresses.
You could give them a cheap palisade building which gave bonus defenses.
Defenses are still thoroughly messed up in this mod; many defensive buildings just don't work atm. Its unclear exactly how its supposed to work, but I think it should function like FFH, where all defensive buildings stack and they all stack with cultural defences, rather than in vanilla civ where defenses are pretty useless because they don't stack with cultural defense (it only takes whichever id higher).
-relatively powerful archmage hero with a unique range of Ice spells (maybe 3 or 4 strong ice spells)
Sure.
-strong affinity with bears
Implemented how? Thats part of why I like a beast-magicy shaman unit with some of the bear-oriented spells.
Remember that you can still use the existing spells and techs without necessarily thinking of them as still being winds magic in the same sense as mages.
So you could take away hedgewizards and such, but allow them to research winds of magic and lore of beasts tech in order to be able to build some units and get beast spells. You could have a priest unit that requires Lore of Beasts tech and priesthood tech, that can cast some beasty spells. Call it a priest for fluff purposes, even if it uses the same promotions in theory as a mage.
Elemental magic is exactly the same, if not the same, canon made no distinction between them
Ok. But we can still use the existing techs and spell promotions to replicate the idea of a priest with supernatural beast/nature powers, even if these aren't actually magic in the same sense as used by other factions.