I applied through Washington DC, I didn't have to show a plane ticket but they did ask for a flight number. I only showed 1 month of bank statement. I rent a condo, so that was the address I used.
I already had a doctor i was seeing in Bangkok. I just asked her to give me a letter confirming I was a patient of hers and that hospital. She put in the letter 1 appointment in December and it was approved, no questions asked. It must be on official hospital letterhead with the doctors signature. I just said I needed it for my visa, didn't mention what visa I was applying for.