What I would like to say is that I think the Warring States would fit the campaign mode for China at that time (they have different general leaders and units, but basically follow the Han structures), since apart from special units, leaders, etc., I don't think there would be many differences from the Han for a separate civ with new structures and units, though of course I could be wrong.
The Kushan Empire was a separate entity, more closely linked to India, and was essentially considered the leading power in Central and South Asia during its peak.