That's about 60 days within the last year. That's not excessive.
Just make sure when you arrive the first time you have your flight to Vietnam ready to show if they ask about when you are leaving. And then the 2nd time when you return from Vietnam, make sure you have your flight back to South Africa (or wherever it is you are traveling to next) available in the event they ask that time.
You cannot get a non-OA visa. That visa is only available from the Thai embassy in your home country. But that's okay because you don't want the non-OA visa, you want the non-O visa.
Go to your immigration office and ask them for their handout of requirement to convert to a non-O visa based on being over 50 (nicknamed retirement visa)
Once you have the 800,000 in your bank, you should be ready to apply for the visa, based on the requirements from your immigration office. You should not have to leave the country, as long as your immigration office allows conversions. There are only a small number of offices that do not.
If your office is one of these, then yes you can go to Laos and apply for the visa, but that's better asked separately if that situation comes up.
It's not technical. The government regulation is clear. It has nothing to do with "controlling" the money. It says if your foreign bank accounts holds that amount of money during the year.
ALL 90-day reports are done at the main immigration office now. Having an appointment will allow you to go to the front of the line. I believe it's on the 3rd floor now, as it just moved.
No. It absolutely cannot be in your wife's account. And as far as joint account, you have to check with your immigration office. Some would accept it, while others will not. If your office does accept it, you must have double the required amount in there, since only 50% of it is considered yours.
An agent won't save you from this. The requirement to file an FBAR is if you had a foreign account that was over $10,000 at any point during the year. Using an agent, they put 800,000 baht into your bank account and then remove. Therefore you had a foreign bank account greater than $10,000 during the year.