Not unless your embassy in thailand does income affidavits. If they don't (which most don't these days) you will need the 800k for the first extension.
That is your 90 days notification date. 90 days is called a notification of residence. You get 15 days before and 7 days after to report. After those 7 days you are fined 2k.
As for what documents you need like everything, it widely varies office to office, so you should check with your local office.
I've had one in 3 days, 1 in a week and one that took nearly a whole month... like everything in thailand, it really depends on your location and the office being used.
I use skyscanner and the majority of the time Agoda is the cheapest so I end up using them a lot, never had an issue and I fly in and out the country for work at least 2 times a month, most months.
Unless you have a valid and current IDP and licence from your home country that indicates and shows you can legally drive a bike, you will need to sit the Thai training and tests. (Not sure how long they take because when I got my Thai licence I had a valid and current IDP). The 5 hours is likely the theory lessons and test.
Brandon is right as always... Non-RE means non immigration reentry, No one is putting non-RE as a non-o retirement, if it was a non-o retirement it would say Non-O, not non-RE, which means non-immigration reentry nothing less and nothing more and is only used as a reference for all non-immigration reentry permits 🤦