Passport, current Thai DL, Medical certificate, application. If you have a 2 year DL and a Non Immigrant visa you can transition to the 5 year DL. If not, you get another 2 year DL.
Yes, most immigration offices issue them that way. 15 days under consideration and then 45 days when you come back. Don't ask why, there's no logic in it and just increases the congestion and work load at immigration offices.
60 days from the date the stamp is issued. The covid unable to travel extensions are different than normal extensions that are issued effective when your current entry stamp expires.