A possible Unit characteristics:

1) Southern principalities has many steppes and fields. Here must be a lot of strong and light cavalry.

2) North-Eastern principalities are situated in land of many forests, they must have strong infantry and medium, but strong cavalry, a few light cavalry.

3)Novgorod is a trade center, it situated in the land of lakes, marshes and rivers. A big role have fleet and infantry, a minimal - cavalry. Long wars against sweden and germans had a influence on Novgorod warfare. Of cource no cossacks