ok guy your the expert. Why would anybody who intends to stay long term waste time converting a 60 day visa exempt entry to a 90 day when they easily get the 90 day ahead of time and convert directly to a 1 year. And why would anybody commit that amount of money for any length of time to a non interest bearing foreign bank account when it's not necessary.
If you want a non immigrant O type of visa then first you will need a Thai bank account in your name, and second the 800K needs to be on deposit for 3 months prior and 3 months post. 6 months total. Most people apply for the initial 90 day visa before they enter and then use that visa as a basis for opening an account. Once the account is open you can make the transfer and continue with the 1 year extension process.
Marriage visa or Retirement visa. You gotta choose which one you want. Cannot mix and match. You can open a bank account by yourself. No need agent for that. The agent is helpful with the 12 month extension of stay to avoid keeping your money locked up in a Thai bank account.
right you open the bank account by yourself using your initial 90 day visa, then bring your bank book to the agent and let them handle the 12 month extension. IMO this is the best way to get what you want for the least amount of cost and time. No insurance, no money needed in any bank anywhere, no background check, and no 90 day nonsense.