Future expansions.

The ancient Slavs had neither castles, nor fortresses, let alone kremlins.

Do you think I came up with the faction name?

And a kremlin in its natural form (just like the Slavic soul) doesn't fit into the Ashan concept at all. And as for creatures, what about house spirits, kikimoras, leshies, and zmei-gorynyches?

No. Just a regular Haven with an East Slavic style. No leshies or gorynyches are needed. It could be something like this:
Basic units:
Support unit - some weak air mages.
Ranged attack - an arbalist or archer made in the style of Ashan's Streltsy.
Melee attack - men with swords or spears, similar to regular Novgorod or Kyiv warriors.
Advanced units:
Elemental - an air elemental.
Ranged attack - the same men, but with some Streltsy muskets that fire using air magic.
Melee attack - bogatyrs. Taller than 1.5 men, with huge muscles, wearing bogatyr armor, with swords and shields...
Champion:
Let's use some creativity here. Maybe some overgrown wyverns (Ashan's Gorynyches).