As for new civs, I think Manchus will also be a good addition to spice things up in East Asia and prevent Korea / Japan from easily expanding into Manchuria,
- also to keep Chinese AI / player busy instead of just chilling after 3 Kingdoms and Mongols
History:
- Sushen = mythical-early contact with Shang → Mohe = real organized tribes during Tang → Jurchens = warlords and founders of Jin (can replace some barbs then) → Manchus = final synthesis and Qing founders.
Spawn:
- suggest later-Tang spawn, giving them more time to conquer north China before getting wrecked by mongols
- Tang should be weakened by Yellow-turban-like barb spawns representing An Lushan rebellion in 755
- at historical time of invasions, gets conquerers representing Jin
- AI should get collapsed by mongols, leaving independent / barbs in Manchuria
- Humans can fight mongols off or just chill in Manchuria
UA:
Qing focused UA can be something boosting tributary-trade, as Qing trade was highly regulated
UU:
- Jin can have access to Oghuz as another expert horse-archer civ
- Qing Eight Banners Cavalry (replaces Knight or Cavalry)
UB:
Jin Fortress (replaces Castle)
or Qing Imperial Examination Hall (replaces Courthouse)
eg UHV:
- Jin: Control Manchuria and North China by (sometime before mongol spawn)
- Qing: Historical max territory: Mongolia, Tibet, Xinjiang, Taiwan by (reasonable time)
- All under heaven: Some population % goal, settled great people goal, tributaries goal etc