I was here on a retirement visa from 2011-2016. My wife and I got married in 2016 and then she applied for a Green Card at the Embassy. This was granted in July 2016. We then moved back to the states for 5 years which turned into six. This was to satisfy the five year joint residency requiremet for my wife to be my beneficery when I die.
We returned to Thailand at the end of Septemer 2022. I came in visa exempt and they stamped a 30 day visa. I got a 30 day extention and at the same time started the process for a O based on marriage.
In Chiang Mai, the first thing you have to do is deposit TB 400K in a bank (mine is BKB). There is no exception to this, save maybe if you are on an elite visa coming in. You then get a certication letter from the bank that you have the money in a "Fixed" Account." My current understanding that you have to leave the money in the bank for one year, After that there is no requirement since you have proved that you get at least TB40K every month. But it could change.
As you wind through the process, make sure to bring your Thai wife with you every time you go to immigration. If she is familiar with the process, let her do most of the talking. They are trying to confirm that you are not in a "sham" marriage.
The reason for the 5 year joint residency requirement is due to thousands of Vietnamese women paid Americans to marry them and get them to the states where they disapeared. I really am not sure why the Thais are so concerned about this, but money is at the root. Someone at Thai immigration told me that they would prefer if I applied for a retirement visa again (more money required in the bank).
When we finally got our home vist from immigration, a lot of time was spent explaining a new rule, that I still do not understand,
If you have no experience doing this, I would recommend that you have a law firm or other entitiy walk you through it and do all of the paperwork. It will run you TB20k to 30K. I used Siam Legal, and they got it done.
Good luck