Go to AIS with your phone and your sim and your passport they will give you a receipt showing your phone number your passport number and your registered name then you take that to Bangkok Bank and make sure that everything syncs. They also want to see the confirmation SMS
The application form asks for intended or proposed flight and date it doesn't mean you have to buy a ticket, you're under no obligation, the same with your accommodation just put the first hotel you're going to stay at the day you arrive
If this is your second report you are now on an extension. To avoid confusion and to obtain relevant advice in the future, state you're on a non O over 50/retirement extension.
What a mess, please state the validity of the visa, when is the 6 months finished? Nevermind your last entry stamp date. By re-entering Thailand just before the visa expires you can get another 60 day stamp and extension in country, getting almost 9 months out of the visa.