Chiang Mai is cooler weather. Prepare for smokey season end of January through April. Many will relocate to the south during this time.
As long as you have your work situation and education for the kids figured out this move can be done. Our family of 5 move next week to Thailand from America, but I am Thai so the approach is different. There are somethings I can guide you on to make your transition smoother. You may want to look into a DTV visa for all adults, kids can be in the country.
After reading all the comments it appears you do not need 400k Thai baht in a bank. But, what does need to happen that is accurate. Husband needs to exit on US passport ' and reenter on his Thai passport. Then according to some people's comments here you can get your US marraige certificate certified in Thailand for MFA, but unfortunately I am.not familiar with that process. I only know the channels how to get your US marraige certificate legalized in the US. Maybe that person can provide the steps how you can legalize your US marraige certificate within Thailand so it can save you some time. I wish you two the best of luck and enjoy your retirement in Thailand.
The process is actually very simple and you do not need an agent. The husband needs to re enter on his Thailand passport and not a retirement visa.
Step2. The Secretary of State needs to certify your marriage certificate.
Step 3. Then your marriage certificate needs to be sent to the Department of State in Washington DC to be authenticated.
4. Next you need to send it to the correct Thai embasy to authenticated the marraige certificate. There are several locations. Washington Thai Embassy, NYC Thai Consulate, Chicago and California embasy.
After you receive your marriage certificate back with all the Authentication. The document then needs to be translated into Thai.
I recommend Sawadee Transportation located in Bangkok. This office will also have the MFA certify the document for you.
Then the final step is to register the marriage at the local Amphur building.
I recommend this over the retirement Visa since you are married to him it is much easier.
Hello I can assist you with understanding the steps to properly be in the country given he is a citizen and your legally married front the US. Feel free to PM. I typically work with adoptees reinstate their citizenship but I do understand your situation and the proper channels you need to do.