I first got the O-A visa. It took about 2 months from start to finish. But if you can just get a physician to sign the medical certificate then you can knock off 3 weeks. I spent nearly 800 USD and waited 3 weeks to get all test results back to get the document signed. Other people said their doctor just signed it for free in seconds. The next time I got a "retirement" visa I just arrived non exempt and I paid a reputable visa agent around 25k Baht to do all the paperwork. I used Wise to transfer the 800k Baht. This is the simplest but most expensive option.
You might look at the O-A Visa. I had one of those back in 2019. I hate leaving 800K baht in the bank. The O-A requires insurance (not in 2019 though) but then I personally require insurance so that's not a drawback. I use a plan from April Intl which is probably not approved (yet has 1 million USD max per year) so you might have to buy some worthless plan but that just goes into the cost/benefit analysis. Leaving 800K baht in the bank has a cost. One downside of the O-A is the medical certificate. I had no primary care physician and could only find passport health to sign it at a cost of around 700 USD and 3 weeks of time. Plenty of people said their PCP just signed it. I actually got a lot of tests. You can get 2 years out of the O-A and keep your money working (hopefully) back in the states.
Assist Thai Visa is legitimate. There are many legitimate agents. I used and continue to use Assist Thai Visa. I have other things I like to do more than dance to bureaucratic rules. The agent reminds me of when 90 days is due, when I have to do the extension and make sure the right amount of money is in the account etc. I use them for everything that I find tedious and boring. Granted, other people people prefer to save the money and do it themselves. To each their own.
This group is rather general. If you want to do the visa route yourself, I highly suggest using the Thai Visa advice group. The admins keep everything focused and current.
You didn't ask about the O-A Visa but after reading your whole post I think you'll be much better off with this one. Your money remains in the USA. I pulled money from investments and put it in my bank account and took a screen shot of it. My bank would not verify anything. Do you have a primary care physician who can sign the medical certificate? I didn't and paid over 700 USD and waited about 3 weeks for all tests. But most people just have their doctor sign it. You'll need to buy insurance. But this one really looks best for you. It will give you 2 years if you play it right.
Did you do it by talking to someone at the bank or just use their app. I have Schwab primarily for the ATM but used BoA for the transfer. Does Schwab show you what will happen before you commit like Wise does? Thanks
I experimented with my bank in the USA and Wise. I used the form in the bank app to send the money. It was confusing and opaque. Wise was not only simpler but it showed me the details including how much I would actually receive. It compared itself to it's competitors who sometimes would be a better deal. The amount I actually received in Baht from the bank transfer was a few percentage points less than Wise. And the only way to know that was to do it. I always, always use Wise.
You really want to study the Thai visa Advice group. It is excellent. I'd spend at least an hour persuing it, probably 2 hours. Personally as I've used brokers in import/export many times I have nothing against brokers and appreciate their knowledge and am happy to pay for it to avoid bureaucracy which I despise. But I read this group to know what's going on and I appreciate the attention to detail. BTW, it's not cheap to pay a broker to do this but it makes it easy.
Do yourself a favor and post to the Thai visa advice FB group. The admins are nitpickers, pedantic, detail oriented, just the sort of people you want to listen to.