I entered last week. You do not need a return or onward flight. I presented my passport, a laminated A6 copy of my DTV and the boarding card of the flight I arrived on. I was stamped in under a minute and complimented on my laminated DTV. She said it was so easy to scan and wished everybody did that.
They prefer a hard copy of your DTV. You do not need a hard copy of the TDAC unless it is your first visit to Thailand. I printed my DTV A6 size and had it laminated. The IO was very impressed and called a colleague over to show how easy it was to scan. She said I wish everybody would do this. I know we live in a digital age, but unfortunately, not everybody does.
In the UK, you do not need 800,000 baht to get a non-O. I have applied for 3 over the last 5 years and have never had more than 40,000 in my bank account. However, you will need 800,000 in a Thai bank account for 2 months before you can apply for your yearly extension, so if you do not have a Thai bank account, it must be the first thing you do. No insurance is necessary for a Non-O visa.
You are allowed to use your IDP for 90 days, but after this, you need to get a Thai driving licence. You will only get a 2-year licence as you are on a tourist visa. You need to make sure you have an upto date TM30 registered with immigration, and then you can obtain a certificate of residency, together with your IDP and passport, which you need to get your Thai license. You will need a photocopy of your bio page and entry stamp from your passport. If you have a valid motorbike licence, this can be issued at the same time. In Thailand, they have separate licences.
The booths in the exchange zone on level B are comparable in rates to any of the booths in Bangkok. It's the booths upstairs that offer poor exchange rates
I had this same problem on my laptop. I had to slide across to display the upload option, as it wasn't all displayed on the screen. Took me a while to figure it out.