I also got both my Thai drivers licenses, car & motorbike, just using my California drivers license. Get an international license before you come here but no one has ask me about it. I didn’t know they existed before I got here.
1. Make sure you have a reliable means of transferring money to Thailand. Note that not all banks will accept voice over internet phone numbers
2. Passport, drivers license, and credit cards should have expiration dates as far out as you can. 1 year minimum.
3. 2 credit cards from two banks to back each other up
4. 6 months of essentials until you can figure out where to buy what you need. Essentials could be medications or large clothing sizes or stick deodorant or your favorite toothpaste. You can buy almost anything here or online but it may take a while to find out where.
5. Bring some cash to get started. I brought $10,000 long ago. All the currency notes must be new or pristine condition or you will have trouble exchanging them.
6. Bring originals of marriage certificates or divorce documents.
7. I did not need an international drivers license to get my Thai drivers license but many people recommend it. It might be something to look into.
8. It can be helpful to maintain a US address. Use a family members address or a friend. Last resort you can try a mail forwarding service.
9. Unlock your cell phone. I have kept my AT&T international calling plan for 7 years now. I’m glad I did.
In the end you don't have to bring many material possessions. I and many people arrive with just a couple of suitcases of stuff.
I signed up for Social Security when I was living in Thailand and when I turned 62. I used the Social Security office in Manila, Philippines. They also had my address as being in Thailand. A few months before I turned 65 I contacted the Manila SS office to ask them not to sign me up for part B. They said they wouldn’t sign me up unless I specifically asked them to do so. I didn’t ask them but I wonder if they won’t automatically sign you up if they know you are living in a foreign country.
The only difference between the two extensions is the insurance requirement for the OA. You should talk to your insurance company about synchronizing the dates of your insurance policy with the OA extension dates.
Unless you are trying to avoid the insurance requirement you don’t need to switch to a non-O. You can renew your insurance and extend the OA for 1 year inside Thailand.