What documents do I need to apply for a 60-day tourist visa to Thailand in Hong Kong, and is a booked flight mandatory?

Hi everyone, I am planning to fly to Thailand around the 12th this month. I am AUSTRIAN and I am currently residing in China. I would like to apply for a 60 days tourist visa in Hong Kong and also I would like to keep the waiting time for the visa to a minimum, as HK is an expensive place to wait. Does anyone here have experienced a Thai visa application in HK? Also which exact documents will I need to prepare. Is a booked flight to leave Thailand 100% necessary or is their any way to avoid that. I don't know what I am up to after 3 months, so booking a flight now would be a bit ridiculous.

Thanks in advance and happy new year everyone :)