would I be able to buy my round trip airline ticket based on my forecasted 150 day stay? Also, are you referring to this visa? - Non-Immigrant Type “O” Retirement.
I would bring that health form to my doc, he would sign it and send it back to me - no problems. We split our time between Thailand and the US for nine years and the non imm o-a process was not particularly difficult. I just followed the LA Thai Consulate’s checklist. Got a new non imm o-a every year.