Thanks for the suggestions Shadowcry. The ideas on waves are very good, to give a different feeling behind each invasion.
A few things to remember though:
Each mesh is a set of 3-5 bodies and textures which remain relatively similar, but not the same. They need to have a generally similar armor type (Not clothed guys amongst well armored guys, for instance). So for example, the Russian mesh would have to work for both spearmen, Druzhina, and Kazakh horsemen. If you look at other factions, you'll see a single mesh/texture set used for more than one unit: For example in Egypt, the Ajnad mesh is used by Maghrebi marines, Harafisha Infantry, Jund Spearmen, and Ajnad Horsemen.
So when you suggest a mesh, it will need to be utilized by more than one unit with the same texture and appearance. Now, that being said, for Mongolian Auxilia which would exist on our map before their arrival (Such as any Russian, or Turkish units), we can just make these existing units into AOR of the Mongols.
For the Chinese units, we need to have some information showing that the Mongols used a good deal of Chinese Auxilia at least in Central Asia and Iran. We are not too much sticklers for absolute accuracy, and while I love Chinese armor and styles, I would like to make sure that they (Or the Koreans) warrant inclusion as soldiers in the Mongols in this part of the world.