To the OP, from everything I read and see here, things are definitely getting tougher/stricter on the two main issues you raise -- repeat of use tourist visa entries by Immigration, and enforcement against bank account holders who lack long-term visas by the various Thai banks.

Re Immigration, the indications lately are that they want to see repeat tourist visa people having a track record/history of returning to their home country between Thai entries, not just border hopping to some other nearby SE Asian countries. As you seem to be an American, that would be at some point they'd want to see you traveling back to the U.S. before allowing more Thai entries.

Re the Thai banks, it's always a crap shoot, as they're so variable from branch to branch and banking company to banking company. But there definitely have been reports of existing account holders having their accounts closed at some point because of lacking a longer term visa. So relying on only a tourist visa would certainly be a risk, these days.

All I know personally is, every time I have a substantive business with any of my Thai bank accounts, including most recently needing to replace an expiring debit card, they as always wanted all my passport photocopies, and specifically took a copy of my current visa stamp, as they always have done in such cases.

Sorry, I misspoke a bit above... The emailed statement route is via the two banks' Android mobile banking apps... not via their website online banking platforms.

Both Bangkok Bangkok Bank and I believe Siam Commercial as well now have the ability to request 1 year past prior bank statements for your accounts via their online banking platforms. And they'll email you the full statements typically within the same day for no fee. I just did that recently with BKKB when I needed to get a year prior detailed account statement for FBAR purposes. And I talked with SCB customer service and they said they will do the same. My BKKB statement arrived within about 15 minutes after I clicked the request within online banking, and that was late at night after regular working hours.