Another point about the Yuezhi, since the map will include the Tarim basin, I don't think it's necessary for the Yuezhi to be an emergent faction. Before the Yuezhi were displaced by the Xiongnu, the Tarim basin was their homeland:

According to Wiki:
"The first known reference to the Yuezhi was made in 645 BC by the Chinese Guan Zhong in his Guanzi 管子(Guanzi Essays: 73: 78: 80: 81). The dates of this book are disputed however, and it may date to as late as 1st century BCE.[8] The book described the Yuzhi 禺氏, or Niuzhi 牛氏, as a people from the north-west who supplied jade to the Chinese from the nearby mountains of Yuzhi 禺氏 at Gansu."

This would place the Yuezhi around the eastern edge of the Tarim basin and the Gansu corridor. This claim makes sense since the later Chinese records state that the XiaoYuezhi, who didn't flee west after being defeated by the Xiongnu, mostly fled south to the Qiang tribes -- who were located essentially directly south of the Gansu corridor.

Thus I think it would be fair to give the Yuezhi a starting territory on the eastern edge of the map right about where you have the Wusun extending into the Tarim basin.

I suppose we could include a script to simulate their later flight west and conquest of Baktria...

Also on the subject, according to Wiki:

"As they settled in Bactria from around 125 BCE, the Yuezhi became Hellenized to some degree, as suggested by their adoption of the Greek alphabet and by some remaining coins, minted in the style of the Greco-Bactrian kings, with the text in Greek."

I guess this could be used as the basis for possible reforms for the Yuezhi after they conqure Baktria; enableing them to build some Greco styled buildins and mabye units.

I'll try to find some more substantive sources later.