The way you imagined Vaegirs, is quite similar to Russia before Mongol invasion. The best part of its millitary strength were retinues of powerfull nobles and rulers. They were quite versatile, adopting both Scandinavian and nomadic ways of fighting, with, I must say, quite less Byzantine influence. So, this retainers (bogatyrs and druzhiniks) used horses due to long travelling across russian steppe, they were capabale sailors, familiar with bows and light lances, deadly with axes, which were quite different from nordic, especially in late medieval times. Swords were also in use, ussualy imported from west. Scimitars and sabres were more in use after nomadic attacks became stronger after 11th century. Second part of army consisted of citizen militas. They werent so strong during early feudal times (although Novgorod militia was many times mentioned, as Novgorod was always considered strong merchant centre which often opposed authority of monarch), but with colapse of Rurikid power and Mongol invasion, they became stronger, because towns now stood alone against many invaders. Third part of Kievan Rus armies, were mercenaries, usually brought from Scandinavia, but also recruited among northern non-slavic tribes and nomads. I never read about mass conscription of serfs in Kievan Rus, but it seems there are reasons for that: primitive infrastructure and possibility of arming and training them to be capable to stand against nomads, Vikings or Byzantines.
Historical example: during war betwen Vladimir the Great and his brother Yaropolk in 10th century, when Vladimir marched against city of Polotsk, first oponent on way to the throne in Kiev, his army was made from his personal retinue, Vikings he hired in Scandinavia, Chude tribesmen and volunteers provided from Novgorod.
If we talk about Byzantine it is quite diferent and I dont think that thematic organization of early Byzantine armies or Komnenian armies would fit, as I think they were quite advanced to be used as model for Vaegirs. But if you think otherwise, I am open for discusion.
Other slavic countries, those I think were significant during medieval times, have their own millitary traditions. Poland and Czech were quite westernized so I dont think we can find some interesting examples there (although Czech hussite insurgents developed their own tactics, but that is already 15th century, so I dont know should we discuss them? ). Bulgaria in first half of medieval times was predominantly influenced by nomad way of warfare, and later, after First Bulgarian Empire collapsed, they were never big players again. Serbia rose to power during 12-14th centuries, and had its own quite interesting millitary characteristics: it relied a lot on serfs both as mass conscripted army in times of emergency, and as steady source of lightly armed soldiers for troops provided by lords (remote nature of most of Serbia and some ancient tribal influence I think were reasons for that). On the other hand, due to lot of income from trade and especially mining, Serbian nobility often equiped themselves and their paid soldiers with excellent weapons and armors from both east and west.
So this is a little bit of history, its up to you now to say what do you think about it so we can make further discussion.
