Cars are a problem in Chiang Mai -

Pol. Col. Sitthichai: Well, there are two sides to the story. On one hand, I’m happy for the consumers and Thai people because everyone had the chance to buy a car. On the other hand, the traffic jams all over the country as well as in our city have worsened. Since the tax rebate policy there has been an increase of over 50,000 cars in Chiang Mai, a massive number that our roads just can’t handle. The policy had also led to parents buying their children cars so it’s no surprise that the roads are jammed during rush hours. For example, at Montfort College we now see up to 500 students driving cars to class instead of going by motorcycle, which makes that district very busy. Although I must mention that another positive is the fall in the number of motorcycle fatalities.
I would like to see a public transportation system put in place here in Chiang Mai but once again I must point out that we just don’t have the funds for such an investment. The tax rebate policy is also a lot bigger than just making it possible for Thai consumers to buy cars; it must be seen in the context of the floods of 2011. The Thai government was worried that car manufacturers would move their factories out of the country so they implemented the policy. A lot of car owners also had their cars damaged or swept away due to the tropical storms and the government saw it as an opportunity to stimulate the economy and encourage the worried car manufacturers.

From Chiang Mai City Life

As for the choice of Mae Hong Song area or the area around Chiang Rai , Mae Hong Song province has more forest.

If doing Angkor Wat then a small Thai town with temples isn't worth the trouble. Better off doing somewhere like Khao Sok np overnight trip to lake area or a multi day trek up north from Chiang Mai or Mae Hong Son.

Its been done for more than decades . But that's not the point . Conditions recently have been more extreme than usual. I have been in Chiang Mai and the north a number of times and didn't have to wear face mask. Its been measured for years but most years it doesn't get to the stage where its the most polluted city in the world briefly.

As for being prepared and knowing what they getting into - fine words in theory but things don't always work like that it reality.

Thank you very much for all the information. Very helpful.
So to summarize, it's either the international bus on Mon, Wed, Fri or Sun for THB1.500. But can't book in advance.
Or fully travel by local public transport which seems relatively cheaper (CM to CK THB202, crossing THB25, tuk-tuk KIP25,000 and bus to LP KIP130,000, a total of about THB800). I suppose we do not book that in advance either.
Finally, I recently found this "tour bus" which also goes from CM to LP for THB1,450.
https://www.travelhubchiangmai.com/tour-detail/tl1001-chiang-mai-to-luang-prabang-by-bus.html
It seems that they run every day, and are competitive in term of price. And I can also book in advance. Have anyone heard about them?

I agree Wonderingtsar2. Our family was more impressed by Bagan than Chiang Mai. We respond to topics because we enjoy sharing our experiences. After 2 weeks of busy travel, Flight to BKK, flight to Siem Reap, flight to Sukothai. flight to Chiang Mai to Mandalay, to Bagan, to Yangon, to BKK, to Phuket. Nine flights in 15 days. Thenn a week of rest in Phuket on the beach. No one is obligated to fly so much. Sometimes flying gives you more bang for the buck. The OP is saying 8 flights in 11 days. It's his trip not ours. I have also gone to places on long bus rides, only to be disappointed.

I did 2 nights in Mandalay one day car and driver there. Flew to Bagan, one night was enough and toured a whole day. Then on to Yangon. Chiang Mai is not what it used to be for so many days. 3 nights in Luang Prabang was enough for me. Siem Reap in fine, just came back. I agree with Wanderingstar about Bagan. It got hit by an earthquake in 2016, so who knows how long everything will be there. You could fly from Mandalay to Chiang Mai and on to Luang Prabang then to Siem Reap on Lao Air. Do Yangon/Bagan/Mandalay.