I could give you pretty good beta on all your destinations, I'd go to China first and let Thailand and Vietnam cool down a bit. China you can check out Yangshuo, Getu, Kunming, Dali, Liming for starters, if you come to Getu and Kunming I have loads of local beta including new crags etc. Travel, food and accomm' is easy and cheap, language is always an issue. I'd do vietnam second, easy to get overland transport from china (cheap and nasty). Cat Ba in Halong is great but also some new awesome crags north of hanoi, check out Vietclimb, they pretty organized. If possible go to Loas as well, perhaps skip Vang Vieng (unless you like drugged out backpacker idiots) and go straight to Thakhek (google "green climbers home"), the place is amazing, climbing is awesome for all grades, cheap. Then thailand, south of Thailand is well established, new development though at Koh Yao Noi worth checking out (great climbing, no crowds), but not far from Laos, in Northern Thailand you should stop in at Chiang Mai and Chiang Dou, definitely worth a visit.
Let me know if you want more specific details.