As far as I'm aware you can't get a permanent residency. You will need a work permit for any form of teaching. Most schools will only give you this if you have a degree. Be aware that some schools are also very ageist. Good luck. I hope you find what you are looking for in Thailand 😊
Inmigration is closed at weekend so providing he goes tomorrow he should be fine to extend. I think I'm right in saying if the stamp is a weekend you are ok to go on the Monday