I would check with the airline that they will let you board knowing you have a return flight after the visa exempt runs out. They can ask you to have an return flight or an onward trip within the 60 day visa before they allow you on the flight, so i would check before you go to the airport
To be fair it has been taking typically 14-16 days recently at the London embassy, but certainly is worth an email if you get concerned since they always respond
You may have no choice but to try and enter on visa exempt (could be ok certainty for the 60 days with no extension) because it has been taking between 14 -16 days to get a visa through the London embassy ( assume thats where you are applying)? . Good luck 👍
i would hope you will be ok for your next visit although as you know it will be up to the immigration person as you arrive. If you dont want any of the worry you could apply for a tourist visa through the evisa online system which would give you a 60 day stamp when you arrive, you would then have no problem entering
The non O dates you have been given is the time you have to enter thailand I.e. 3months. When you arrive between these dates you will be stamped in for 90 days, if you want longer then you will need to open a thai bank account and deposit 800kbaht for 2 months before you can apply for a year's extension
All I would say is if you have the time then I would just apply for a tourist visa then y9u shouldn't need to worry. With the changes currently taking place you only need an excited immigration officer to give you are hard time based on how they feel!!. Good luck