If you do choose to stay in Thailand after 2 years and do yearly extensions of the OA then you have to investigate the validity of your home country insurance. Chances are it won’t qualify.
Eight years ago I walked into a Kasikorn branch, Phra Khanong, Bangkok, on my first day in Thailand with my Thai girlfriend. I had a new OA visa in my passport. I opened a bank account with no problems. My girlfriend told them to use her address.
Last October I opened a bank account in Bangkok Bank in Sisaket province. This time I had a yellow book and an LTR visa. I opened an account with no problems.
It seems to be much more difficult for newly arrived expats these days.
I hired a tax legal firm this year to do my 2024 US taxes. The firm is familiar with the tax treaty between the US and Thailand. If I was paying taxes in Thailand I would let them handle it.