It has been a while since I read my Kalevala but it has a lot of things which could be used as heroes/spells/summons/items. For basic unit lineup you can look info from other sources. Some light/medium infantry would work fine. For example something like hirdmen & huskarls of Vanheim with axemen and shortbows/villains. Hakkapeliitta as a light/medium cavalry. Maybe even make them sacred, at least I can't think any other sacred unit apart from some which would work better as summons.
Commander roster is a bit more difficult tho... forester, hakkapeliitta commander, wiseman/singer and witch spring to my mind. Wiseman is mage-priest with NNEH and some randoms, like water/death/fire for example. Witch could be almost the same but without priest skills.
As spells and summons diseases and all sort of spirits of rivers, lakes, fire, dead people, forests and so on are pretty common in finnish mythology. Also spellsongs and animals (bears, wolves, swans) are obvious. Making dom spells out of those requires creative imagination and work with stats and abilities tho.
I would certainly play a Kalevala mod.
