Southeast Asia forum

If you are not prepared to spring for flying from Laos to Cambodia (there are no cheap flights) then you need to plan about eight days to get to PP, with a stop at Siem Reap along the way. You can bus down from Vientiane, stopping to see the Kanglor Caves in Tha Khek, hit up Paxse, go over to 4,000 Islands and then cross into Cambodia and hit up Siem Reap. Then go from there to PP. After that (or perhaps before, after hitting Siem Reap) I would go to Thailand and maybe go to a beach somewhere south of Trat. Perhaps Koh Chang.

Guangzhou > Kunming and Dali
Dali > Luang Prapang, Vang Vieng, Ventiane

Are you taking a train to Kunming or flying? Dali isn't really the highlight of the region - will you be going up to Lijiang area as well?

The bus route from Dali to Luang Prabang is a long one. It'll take a full 15 hours to get from Dali to Jinghong and you'll probably want to stop for a night at least there before heading on from Jinghong to the Laos border - Xishuanbanna isn't a bad region if you know some Chinese and want to rent a bicycle and travel around for a day or two, but I imagine you'll want to pass right through with your schedule.

It's been a long time since I went from Jinghong to Luang Prabang, but I stopped for a night in Udomxai - I've heard the roads have improved a lot though so you may make good time. You could also go to Muang Sing or Luang Nam Tha upon crossing the border to do some trekking and then head down to Luang Prabang, but again I'm not sure if your schedule allows for that.

So - you've got about 6 weeks it looks like and 2 of that is set aside for either Cambodia and/or Thailand beaches. That gives you 2 weeks for Yunnan and Northern Laos and 2 weeks to get from Northern Laos down through Cambodia to your departure from PP. If you spend just two nights in Kunming (stone forest and other day trips) and then 4/5 nights in Dali-Lijiang area you've got to hurry through Jinghong (not a bad idea since you'll see a lot of the same in Northern Laos) and then you could have a week in Luang Prabang/VV/V with some overlap into the two weeks given over for getting through Cambodia. If you take roughly MADMACs 8 day plan you should have plenty of give in your schedule for at least a week at the end of the trip for some beach time in Ko Chang area before the 8 hour bus back to BKK and probably a couple nights there.

Looks like with a schedule like that you'll need to rush from Dali to Luang Prabang (can be done in 2 full days of bus riding) to make sure you've got enough time to stop throughout Laos and Cambodia on your way.