It takes 2 months for turn around. When I came here on exempt i started it my first week and it came back a week before my exempt stamp would expire ( didnt extend )
School will send off acceptance letter and request to the ministry of education for permission to study.
If accepted you will then goto immigration at index mall with paperwork to be placed under consideration ( process time to grt visa ) you will be given a date to return to immigration by the airport ( main office ) where you will get your 3 month stamp
That you extend for another 3 months for 1900 baht will do this 3 times and still do 90 day report ( based off your education visa stamp )
possibly but if he can show he appeared to extend stanp but full book may not depends on IO and the pull of his ambassador. Then again they advise and warn everyone to make sure your passport is at least 6 months valid and have pages left, so you maybe right.
The seasoned account is dependant on embassy you use honestly seen people get by with 1 month statement. If you are worried about visa exempt and want to season your account anyway, apply for a student visa to get in selecting thai boxing cooking or language as a suggestion, then after the year is over upgrade into DTV
Or you dont have to wait the full year and process upgrade in the middle but you will have to leave thailand for DTV anyway, why I suggest waiting for the year to end ( you would have to leave anyway )