Go to CW Office to apply for your 90 Day Non-O (Age 50+). You have to show proof of 800K THB (No seasoning required when applying for the 90 Day). Go to your Local Bank and obtain a letter to prove the 800K THB came from abroad. A copy of Bank Book (updated on the day of application). *Passport (copies of Data Page and last entry stamp). *TM-6 (Departure Card) * Pass Port Photo size 1X * TM-87 Form filled out. *2,000 THB fee. They have some Banks ( I don't remember all but I know Krungsri for sure) and a copy center located on the Basement Floor at CW Office.
Yes, Visa exempt gives you 45 Days then you can apply for 1 time 30 Day Extension. During that time you can search for a school for your Education Visa.
If you want QUICK I recommend entering Visa Exempt then you can switch to a Long Term Visa later. Book your ASQ and purchase Covid Travel Insurance. Enter this information to get Pre-Approved COE. AFTER you get COE Pre-Approved then log back in and enter your Airfare and ASQ information to get your FINAL COE Letter. Lastly, get your RT-PCR 72 hours before departure. Good Luck.
As far as I know, Chiang Mai is not on the list. But there is a Thailand ASQ group you can join for more information. They also have "Sand Box" options like Phuket and Samui if you don't want to do ASQ. Good Luck.
What passport do you have? I ask because Thailand has a list of countries it allows to enter Visa Exempt. Your documents sound correct except make sure your PCR Test says "RT- PCR". That was a big deal at the time.