This mod is a dreamed one for me, thank you !
But I noticed a few inaccuracies -sorry if it has been already said. Avars didn't exist
per se in 480 : they arrived in Europe only in the middle of the 6th century. In fact, Avars probably have to be identified with the proto-mongolian Rurans (chinese Ruan-Ruan), who forged an empire in Mongolia in the 5th-6th centuries. Though this hypothesis is discussed, Avars were probably a part of the Rurans who fled the Türks, who had overruled the Rurans in Mongolia. Türks then arrived in Central Asia and in Pontic region pursuing the remnants of the Rurans, who were pushed in the Danubian region, where they etablished the Avar khaganate. Instead of them in the Volga Bassin, at that time, were oghuric peoples as Onoghurs, Kutrighurs, Utrighurs, Bulghars and Sabirs (who are already implemented). So imho, Avars should appear in game as an invasion in the Volga. Just as the Turkic Khaganate in Central Asia, btw : is it in your plan to implement the Western Türkic Empire's invasion in the Hephtalites' era (that would be great) ?
About this last ones, I read this comment :
Hey, so some thoughts on the cultural and religious distributions of Central Asia. You've greatly overrepresented the Tocharians, who should be limited to the Tarim Basin. They were also Buddhist and Zoroastrian, not Steppe Pagan. The areas they occupy currently outside of the Tarim Basin should probably be Turkic culture groups - maybe Turkish or Hunnic - or possibly even Uralic people like the Khanty. They were vassals to the Hepthalites, who were also not Steppe Pagan but a strange syncretic Hindu/Zoroastrian/Mithraism that would be difficult to represent with any of the current religions. They ruled over a Zoroastrian and Buddhist population. The Khwarezmians are overrepresented in the west - the western portion bordering the Caspian Sea would have been occupied by Turkic peoples at this point - and underrepresented in the east - they occupied much more of the Tocharian area. They might be better represented with the name Sogdian instead, a related people who played a more significant historical role, persisted much longer and occupied the majority of that territory. The Sogdians were largely Zoroastrian.
If you're interested in online reading about these groups, here are a couple sources -
The Historical Interactions between the Buddhist and Islamic Cultures before the Mongol Empire by Alexander Berzin
On the Nationality of Hepthalites by Kazuo Enoki - page 46 for interesting information about their religion btw
The Impact of the Silk Road Trade on a Local Community: The Turfan Oasis by Valerie Hansen
It would be in fact a big mistake to create a hephtalite religion of their own. The work of Enoki is now quite oudated (1959), and what he said about their religion is based on his false belief that Hephtalites were of an Iranian-Tokharian stock from Western Himalaya. This hypothesis has been crushed by Etienne de la Vaissière in an article pusblished in 2007 (which can be read online :
https://www.academia.edu/1476531/Is_There_a_Nationality_of_the_Hephtalites_). Hephtalites were Hunnic groups from the old Xiongnu empire and who migrated in Bactria from Altai in the middle of the 4th century. In other word they were Turkic (or less probably proto-mongolian), and more precisely Oghuric. And if we read the chinse sources cited by Enoki page 46 of his memoirs, there is absolutly no ambiguity on the fact that it contains a description of a tengrist cult, similar to the traditional turkic-mongolic religion which has its roots in the Xiongnus, and not of a strange hindu-zorastrian melting-pot. In an other way, buddhism may have had an influence amongst them, espcially among ones who were established in Western India and Afghanistan, but we know very few about that, and about Hephtalites in general.
Indeed, Khwarezmians were established in the Amu-Darya's delta, and they had their own independent kingdom in this area. Sogdians were divided in a lot of oasis-kingdoms (in a certain point of view, we could say that Khwarezmians were a sort of Western Sogdians, centered on a larger oasis-kingdom, just as the Macedonians were a sort of Northern Greeks during Antiquity), though a theoritical unified kingdom of Sogdiana existed (maybe a titular kingdom ?). Both were indeed largely zoroastrian, but they didn't practice the same zoroastrianism than the Sassanid Persian, as they never had been conquered by the Sassanians. As the persian zoroastrianism was quite a monotheism (were all the old pantheon of gods became lesser angels), very centralized, with an organized clergy, and was iconoclast, the sogdian one were polytheistic, iconodulist, totally unorganized, with patron deities for each cities. May be it could be represented by a zoroastrian heresy (Sogdian Mazdeism ? Central Asian Mazdeism ?).
Buddhism, manicheism and nestorianism were also well represented sogdian merchant communities, and sogdian trade was very important among all Central Asia. It could be very interesting imo to implement this sogdian trade by a system based on the jewish communities, with small sogdian merchant communities which would established themselves in your domain and with Buddhist or Manicheist Sogdians characters who would pop-up in your court.
Just a few ideas... I'm working on Central Asian history, espacially on Central Asian Nomads' History, so if you need a little help about this part of the map...
Again, thank you for your work, this is a hard task ! Good luck !