A quick update.
No real surprises, the bank actually knew what was needed 🙂
Did the letter the day before going to immigration and a passbook update on the way there (after withdrawing the $$$ to pay immigration).
Interestingly, this year there was no home visit (Pathum were known for visiting every year for marriage extensions) but they still needed a new TM30 address report (I'd left the country earlier in the year, maybe that triggered it).
There's also a handy-dandy way to check your application status using Line.
Works OK, although it just says "Pending" until the actual approval comes through.