An IDP is simply a translation of your government issued license.
You CAN take a motorbike course in Thailand that will enable you to get a motorbike license, but if you're in the US still it would be better to get it there.
Result times depend on how busy the lab is. Now there's not a lot of people being tested (especially in the west were most are vaccinated). Should have same day results Most places.
OA visa can only be obtained in your home country, not in country. For the initial OA, the money can be from a bank in your country, doesn't need to be a Thai bank.
A Non-O based on retirement (90 day visa) needs to be in a Thai bank. It's really not hard to open a bank account, you just need to use a bank that works with forigners often. Money shouldn't take more than 3-4 days to transfer.