[Nerfix]

I think the Eras place their own limits but why not have Fewnland as a full-fledged mod-nation in Dom III?

Barbarism, strong shamanism, summoning of otherworldly creatures from the Lake and the Northern Fires and the Sampo would be producing wealth for the nation in the early era.

The middle era would be like my suggestion now and the late era would be a bastardized version of Imperial Sweden with better infantry units, Pikemen, improved Hakkapelites, sacred Lifeguard troops and very puny priests and fire/air mages.