exempt stamp is 60 days. You get at arrival. You only need to provide valid passport, where you're staying, onward travel ticket and 20,000 baht. Most of the time they don't even ask for most of this. π
Yes, a background verification letter from California Dept of Justice (it's easy), there's a vaccination part (that is stupid, my doctor's words). Insurance I used LMG. Was under $400 for a year.
No credit check / history.
I as a residual accrued interest from my bank on the same money that would have been sitting in a Thai bank rotting away. Almost enough to pay my rent. ;)
after that first year there are ways to use things like wise to mark a 65,000 baht transfer monthly as international and go from there.
Critical part is establishing a Thai bank account (not easy lately) and you still have the alternative of the OA and you will not need to keep your money in a Thai bank, just show a balance in a US account. More paperwork, required insurance but otherwise cheaper and safer for your first couple of years. What I did. π