Pure light cav has issues due to tactics changes some patches back, thats why theres some reccomendation to mix in 10-20% Heavy Cav so the LC doesnt fire off Disorganised Harass, the tactic that was added, although in the early game the pure LC composition is more important since disorganised harass, while not optimal, wont wreck you compared to other factors.
CM start Mongols has much difficulty since you start as a Tributary to the Uyghurs, walled by the Uyghurs and their other Tributarys, and the Uyghurs/Tributarys are all Manichean while you start Tengri, which means if you war any Manichean Nomads the Uyghurs will side against you due to religous reasons, or stay neutral and never accept the CTA.
one way of mitigating that is to Convert to Manichean, but you lose the Light Cav combat bonuses that the Tengri faith has as a passive(which is actualy a combat edge against the Mani hordes and something all the other Tengri Hordes have.) the other way is clever diplomacy, keeping a good chancellor parked on the Uyghur Khagan will make him more likely to accept CTAs on targets that arent manichean and less likley to intervene in wars with the other Tributarys, and you can ensure the Uyghurs dont intervene if you get them involved in a seperate war, they cant accept CTAs from their other tributarys if they are an active ally in another war.
if you do have the Uyghur khagan intervene, its may not wreck your conflict with the other tributary since the Uyghur khan is fighting by himself without his khans, and at the start the Khagan is weak compared to his Khans
Early targets as the Mongol Bayads are any direct neighbors you have and any tribals that you can subjugate, you used to be able to subjugate the Khotan area but Pdox added restrictions to the CBS that require certian population and prestige levels so you cannot target feudals and tribals easly as a small nomad, although tribals have lower requirements to subjugate.
i think staying Tengri is worth it, as soon as you reach parity with the Uyghurs you can club them over the head with your combat bonuses and maybe some alliances with the Turks, Bolghars, or Khazars
also, for those who dont know about this nomad mechanic, newly created clans get the their nomad tech and buildings from the tech levels of the province you created them in, so if you make a new clah in a Khotan county that has much higher tech compared to Uyghur/Mongolian kingdom, the new clan may start with better free buildings compared to you, always try to create clans with tech levels equal or weaker than yours unless your confident you can keep them appeased.