If the council feature is too hard to implement,you could create something like this:you could be made the king's adviser and help him in things like:which castle\city to attack next,which lord to favour(gonna talk about this in detail afterwards),which law to pass,which lord to promote(gonna talk about this too),etc.
Lord's Favour:
You could create a system of favours where each lord would strive to win the king´s attention.The king could reward a noble with money,lands,a very rare type of weapon\armor\horse,elite troops,a promotion,etc.This would be given to lords who had distinguished themselves in battle against a superior army,success in an important quest given by the king(or you),captured a strategically important castle\city,etc.This would be useful to appoint the new marshal or admiral(and not electing him like in native),to choose the new counselor or other things you come up with.
Promotions:
There could be a rank system in the army and navy.A system like:Ruler,Marshal|Admiral,General,Colonel,Captain,Lieutenant.The colonel,captain and lieutenant would most likely be in command of scout parties,defending key positions or escorting caravans.
Player Given Quests:
The player could give quests to lords or generals in case they lose an important object(like when you are defeated or robbed),need new recruits and cant´t waste time gathering them and other things.
Naval Battles:
There should be naval battles as they where very important in this era.But,do to the characteristics of china,they should be in rivers.You could make big,large rivers where the battles would be fought.This would also be a very important strategic element in the game as it would allow kingdoms to launch amphibious attacks on the enemy or sneaking up the river and attacking them from behind.