I'm in the process now and you need to book the ASQ hotel FIRST to register with the embassy, kind of a catch 22 situation. Then apply for registration and flight hoping you get one on the date you have a hotel booked if not you can change the booking date. They are not going to let you on a flight without a quarantine hotel to go to. There are only 150 seats in total for the three flights per month (from UK) and you need to book the hotels a good bit in advance unless you can afford the top of the range hotels which are starting at over 220,000 Baht.
All efforts to return must be made through the Thai embassy that is in the country you are in. I had to leave my wife to go to work in Nigeria but as there is no access to the Embassy I had to go to UK to apply at the embassy in London. I went for 4 weeks work. IF and it's a big IF I get on the list to go home to Thailand it will have been 8 months away from home. Good luck!
Well done. Going through the process myself. it's a bit hit and miss due to the tight schedule. on announcing registration for expats the registration system is full same day so you need to be quick and ready.