In Thailand the vehicle is insured, not the driver. You'd have to read the vehicles policy to see if it limits the insurance companies liability if the driver is unlicensed.
There's no such thing as an international drivers license.
-No, you can obtain a Thai license at any DLT, but you need a certificate of residency and immigration only issues those in their own province (Bangkok won't issue you a CoR with a Chiang Mai address).