Thanks to this group (and Dianne Lee who originally spotted my question and clued me in on the Non-Immigrant O-A visa option), two very grateful 50-somethings have their visas!
I want to acknowledge Tod Daniels, Robert Lagas and the moderators, along with the members who are committed to providing no-drama, practical, accurate advice. What really helped make this easier was what I learned from this group: Choose the visa pertinent to your purpose without trying to skirt the rules. Also, over-prepare when it comes to paperwork.
The one question I still had until the end was the "authentication" process for the criminal background check. From the USA to Thailand perspective, this ended up including getting the background check results notarized, then getting a county notary seal (notarizing the notarizer!), then getting "authentication" from the Secretary of State of the state you live in (this is called an Apostille for a Hague Convention country, but Thailand is not, so it's an Authentication and is basically a notary (state) of the notary (county) of the notary (local)). Some of you didn't need to go this far, but we did because the wording on the Thai Consulate website was vague.
Also, we got both a bank letter AND a bank statement. The Thai Consulate website just asked for one copy, but they wanted 3 copies, just like everything else. They only kept 2 copies of completed paperwork (they do want everything colated!) and we think the 3rd copy is because they want us to keep a full set of our own copies.
Traveling to the Thai Consulate was easy and there were almost no lines. I liked that better than parting with my passport, given all the things we needed the passports for to prep for this trip.
I highly recommend making a checklist (we made the one below) with the items on the Thai Consulate visa requirements website for your country. It kept us on track and helped us keep going, even when it seemed overwhelming.
OK, this is a long-winded way of saying many thanks -- khob khun ka -- to everyone who helped to make this process easier!
TLDR : Answer Summary
The author expresses gratitude to the community for assistance in obtaining their Non-Immigrant O-A visas. They emphasize the importance of choosing the correct visa based on purpose and the necessity of thorough preparation, especially concerning paperwork for criminal background checks. They detail the authentication process required for their background check, the importance of having extra copies of paperwork, and share their travel experience to the Thai Consulate. Additionally, they recommend creating a checklist based on the visa requirements to stay organized.