I'm a bit of a three kingdoms wackjob and general history nut so I can give some insight here.
But yeah, unit wise ancient China will probably have just the standard variety of units. Though I don't think it'll be any different from Rome 2 though. Except with shittonnes more crossbows.
Warfare in 220AD China involved almost entirely peasant levies led by small bands of trained fighters. The generals would usually lead these peasant levies by example from the front and the side with the more... "Valiant" general would be able to motivate his band of rabble to sweep the enemy from the field.
This is why there were so many duels during that time period. Because while there might have been 70,000 men in the battle (or 1,400,000 if you believe the Three Kingdoms book), only a few hundred would have been trained fighters. If let's say, Xu Huang defeated Guan Yu in melee combat, the rest of his peasants would have no motivation to fight.
That being said, there are a lot of exceptions to this and ancient Chinese warfare did had some differences from others.
Chief among them all is the fact that the ancient Chinese made extensive use of the crossbow. Even the repeating crossbow got some limited use. This was more than one thousand years before Europe started doing so.
China would equip practically all their levies with crossbows and spears. This is one reason why they had some massive levies to begin with as it's significantly easier to train a peasant to pull a trigger compared to using a spear wall or firing an arrow.
Additionally, if you believe the stuff that's in the Three Kingdoms book, there were some zany units like guys who only carried massive giant shield to form walls in combat, flamethrower tanks (lol zhuge Liang nonsense), chariots with spiked logs tied in between them, etc.
As far as I'm aware, other than the peasants, they did have heavy cavalry of multiple types (this was apparently the distinguishing power of the northern Chinese, think semi-mongols on one hand and classic heavy cavalry from places like modern day Beijing), heavy armored infantry (Cao Cao and the state of Wei really loved these, along with the heavy cavalry), and chariots. Chariots were considered superweapons back in those days.
As for artillery, they really only used small ballista and really rudimentary catapults (like those in shogun 2,). They did have siege towers of differing sorts though.
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tl;dr:
Units in China 220 AD:
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With all that being said, I would like to think that a Total War Three Kingdoms shouldn't involve the units way too much, strange as that sounds. The focus on that timeperiod was mostly on the generals and leaders because the soldiers were all peasants more or less.
That's why a real Three Kingdoms Total War would be about the stories about your individual generals. They'd be the ones charging into battle head first. They'd be the one slaying the enemy general and causing the enemy to rout. It'd be a story about them, their betrayals, loyalties, and individuality. The soldiers and numbers don't really matter because they're all peasants and will flee at the first sign of their impending defeat.
So maybe instead of having a large variety of units, Total War Three Kingdoms would instead have a roster like Shogun 2, but have hundreds of different individual generals and commanders instead.
But at the end of the day, it's just my fantasy.