Screw allying crappythaya or over-worrying about Ming. Improving with Ming will buy you time and you don't get AE with vassals. Grab the friendlies as allies and use the mission on Dai Viet, in my game Champa went in on that which I inherited and vassaled them too. Then I just took claims off of Khmer, Ayu, and Lan Na, later picking up Pegu/Taungu after Pegu joined to help Khmer in its 2nd war. EVENTUALLY, Ming coalitioned me, roughly after they rivaled me because I was among their only eligible rivals lol. Here we are, pretty rich already and about to declare on Ming:
I have Oirat as an ally and they also rival Ming so easy to bring them in. I have a FL of 31, Ming has 44, but it's paper thin Ming troops and I'm tech 7 over 5. Slaughterhouse inbound, and by the end of that first vassal-creating drill I'll have another missionary and be close to Deus Vult to work down some of the Malacca node, though I'll want to vassal feed that a bit too.
Lan Xang is amusing as it's the rare eastern religion that wants religious over humanist. Buddhism has a bit more power than Confucian or Shinto when it comes to conversion (1% more from monastic education), and Lan Xan gets another 1% on its tradition but more importantly +2 TTF so you really want stuff true faith and you have the means to do it. Having only 2 missionaries sucks but we can jack Roma later and until then we can convert some of the harder stuff while offloading more to vassals that are either heresy-cleansed or full annex-released.