1. Small enemies would be great though how they differ from larger enemies will be hard to simulate on a hex grid, my suggestion would be having small units merge into each others hexes to make a beefier unit, i.e Kobold/Sprite + Kobold/Sprite = Kobold/Sprite Duo.
And from there; Group, Gang, Mob, etc. The larger the unit becomes the easier it is to hit, and the more damage it does. When dealt enough damage its swarm size is reduced.
2. I think one problem with flying units is how they might be represented, ideally the difference between a teleporting unit and a flying unit would be that a flying unit can be engaged by archers, and maybe locked into ground combat?? But the art style has a rendition of the upperbody on a pog-like stand, so I’d worry that a hovering unit might look cheap, and might be a pain to find on the z-level plain (like on dwarf-fortress).
In concept though I would love something like that.
3. I would love to see the “Wildmen” used as a bandit sub-faction alongside the “Deserters” and such, since (flags aside) the assets are already on the table. The other creatures you mentioned I’m not so sure about.
I’m pro troll, maybe warhammer-like with health regen, but germanic with fur and nose, with branches they can swing and stones they can hurl. Perhaps in groups of 3, with rare albino trolls that are larger but hate light