@ Hibernian
Cool as always.
Some remarks, though.
Belo Ozero and Rostov might be Finnic with Slavic castles (will it be possible to have different culture for different holdings?)
Moscow and Mojaisk should definately be entirely Slavic. Balto-Slavic hydronyms are absolutely dominant in the area, plus there's a solid archeologic presence of pagan Viatichi kurgans all around Moscow, while we have zero information of any previous settlements there.
Ungvar principality' lands is where historical region of White Croatia, from where, supposedly, Serbs and Croats migrated to Balkans. It's a heavily mountainious region, hence the nomads, be it Avars or Madyars never really settled there. To this day the population of it, apart from the obviously Slavic Carpathian Rusins, is the linguistically Magyarised Slovaks and other Slavs or Vlahs.
Whichever European nomads it was, be it Huns, Avars or Madyars, thier principal area of residence should be
Pannonian steppe (that orange thingy):
This is where they dwelt and from where they raided sedentary areas. On our maps it's where the Blatnograd Principality (or Kocel's Principality) is located, and at the start date. Avars, though, were basically wiped out by Franks, Bulgarians and Moravians by that time.
They certainly don't belong to mountainious areas, like "Abauj".