[Gandalf Parker]

A) the Warlock uses gems which he can find in iron mines, silver mines, gold mines, and even coal mines. A varied number but basically its like a coal mine gives 1 gold, 1 iron, and 1 gem of random type. Different types of gems are needed for different rituals and different elementals. A Gold mine tends to grant more in all 3 things. Nations who cannot use gems will not find them in mines.

B) I think all armies get casters. Some at start and some showing up later. At least some mage mercs can be hired. At that point the "knowledge" of the resources springs up so if its gems, all mines suddenly show gem content and start providing them. If its herbs then all units in the armies (not just that mage) will suddenly start claiming the forests they walk thru and build up a treasury of that.

C) Actually the Troll King always gets Mum at some point fairly early in the game. But he only gets one. However he can hire Goblin shamans, and the more power goblin witchdoctors, who can do a small bit of what Mum does. And he gets access to Troll shamans and Troll witchdoctors. The Troll Witchdoctors can do pretty much all of what Mum does. Including the very important turning of forests into Troll Forests.

D) there is equipment in the game. Swords, amulets, lamps, bottles, rings. They can reproduce spell effects and even summons during combat. Such as, giving your Baron a lamp will allow him to call forth a large Air Elemental during the first round of combat.