Tian Xia has substantive native populations of humans, Ru-Shi dhampirs due to endemic Jiang-Shi vampires, aasimar (there is literally a nation where most people are aasimar), wayang, kitsune, tengu, and nagaji. Oni-Spawn tieflings are also likely prevalent.
As for classes, ninja and samurai would mostly replace rogues and cavaliers respectively. Several bloodlines for Bloodragers and Sorcerers are likely more frequent than in the Inner Sea region (Starsoul and Oni come to mind). White-haired witches are from this region traditionally if I recall correctly.
There is of course for books the Dragon Empires Primer which has some more information on the region.
Give all characters the Civilized trait for free. And strongly encourage them to use it whenever they have questions about eastern culture and honour, because it is quite different from western culture and honour.
Disallow archetypes and classes that do not have eastern flavour.
Clerics: I did away with eastern gods since Paizo was so kind as to provide for Buddhism (Sangpotshi) and Shintoism (Tamashigo). I selected about 10 domains/subdomains for each one which reflected the values of each religion and allow clerics to select 2. For favoured weapons, clerics of Sangpotshi can select any blunt weapon (including improved unarmed strike). Clerics of Tamashigo can select any eastern weapon.
Wizards: Allow only elementalists. The Tian-Shu (Chinese) believe in earth, fire, metal, water, and wood. The Tian-Min (Japanese) believe in air, earth, fire, void, and water.
If you are open to 3PP, I strongly suggest you look at Dragon Tiger Ox from Little Red Goblin Games and The Way of Ki from Legendary games. Since I have incorporated these two into my campaign, I further tweaked the elementalist wizards to require them to take a Monk vow, which combined with the ki feats from The Way of Ki, quite closely mimics the elusive wu jen of older editions.
I hope this helps.