I just got mine, they don’t actually ask for proof of booking. I understand that you can put a flight itinerary that you intend to book. So even the outbound flight does not need to be booked yet.
the bank statement is part of the application, there is a link to upload it. The income route needs 3 uploads, but only 1 link, so need to merge the 3 statements into one file. I did not manage this so they sent me 3 links, which helped me a lot.
I have just done my 90 day None O, I have taken the retirement route, even though I am married to a Thai lady, and have a Thai child. The advantage of doing it from the UK, is that you can use income equivalent to 65,000 baht, in GBP, by showing 3 months bank statements. Or 800,000 baht equivalent in a savings account. I think for the initial 90 the application process is the same for marriage, or retirement, but they do ask you which one you want. When you go for the extension the retirement visa has less paperwork, which is why I am going down that route.
The none O is the one you want for both retirement, or marriage. Also makes opening a bank account a lot easier. I am married to. Thai lady, but I am doing the retirement visa, as a lot less paperwork.
I did 7 visits one year, all for 10 days. No problems at all, not even questioned by immigration. But best to have proof of onward travel just in case.
they sent me an Email asking me to upload more information. When I logged in there was 3 separate links, for the statements that they wanted. I am applying using the income option.