Regarding the topic:
the scheme is almost the same for all races, although I only played through the campaigns where the hero was a mage.
The army composition is as follows: three Fallen Knights, a mage hero, a demon mage, and... who else do they have?
In general, there was someone else, I don't remember.
Although you can take two strong units, a hero, and another unit.
P.S. You should tell us about the initial tactics when the hero has three free slots. Maybe someone takes a strong unit, a hero, and a mage, or two warriors and a mage, etc.