Get a Capital One 360 Checking Account. No fees for foreign transactions including ATM fees and there’s no currency exchange fee.
Get a travelers mailbox/address.
If you’re on Medicare figure out if you’re going to cancel part b.
If you’re going to purchase travel/medical insurance I highly recommend United Healthcare Safe Trip. Depending on what state you’re from you can get coverage for up to 6 months. This will give you plenty of time to find coverage in Thailand. After exhausting research I found their policies have superior coverage with lower premiums than everyone else and they pay directly to the healthcare providers. I have used the policy and it was great.