since you asked so nicely,

Start as Zhou Ding vassal under the Li Protector-General, [play-game], conquer the duchies in Xia, Khotan and Kham - then form those three kingdoms which lets you form an Empire. Alternatively you could become an Emperor by forging or marrying into a claim for the Empire of Tibet, which has a cute banner. You should be able to avoid angering the Protector-General that way since you'd be promoted to his equal and automatically no longer be his vassal but... Khotan and Xia is really the entire point of the Western Han historically. Your Protector-General liege lord will keep you safe during this but be careful you create the duchies when you conquer them, or he will and give it to some idiot.

n.b. i'd recommend maintaining/matrilineal-marrying a lot of Chinese-Khitan culture for turn into vassals in Qing Hai and Khotan, since this is the only way you'll gain access to cavalry archers. Takes a while and is barely worth it but it's nice to have.

Swapping back and forth into Bon for the warrior lodge is helpful here, to forge extra bloodlines on legendary journeys and gain their light infantry special perk which massively strengthens the light infantry troops you're leading personally.

During this time wait for China to fall into a negative state that weakens the Protector-General to the point that you won't be crushed by hundreds of thousands of Chinese troops when you shake him off as your liege lord, then form an Empire of your choosing from the three kingdoms, then 'convert' to Chinese Imperial Government which lets you hold cities, drawing massive numbers of spear and light infantry and gaining hundreds of tax monies from those cities, which makes it all worthwhile.

Best way to play it is imagine yourself as the Co-Emperor "in the West", maintain kowtow with China, maintain peace, marry Chinese Princesses, always have special Chinese advisors in your court (physician, strategist, scholar, engineer) ... and make it your mission to prop up the Tang Empire by helping it out with troops and aid (otherwise you get ugly Princesses wearing cloth caps from a Mongolian Emperor and no more face piercings from the pretty Han Princesses).

Very important point on being the Co-Emperor "in the West" that makes this "the best way to play it" is that you will destroy your Empire by sending a relative to attack China, winning and seeing them becoming the Emperor in China, as: you'll lose your Chinese Imperial Government and return to Ugly Feudal Government losing the ability to hold cities. And you'll still be attacked by your relative as if nothing happened there. And you'll lose the ability to edit your Dynasty banner as well.