outlooks like you need a covid19 test before you fly and a declaration from your doctor your in good health, the post I read said it should be presented to the Tgai embassy in the uk (if your from the uk) suspect in reality it will take a week for immigration to get their act together. You should download the AOT app which requires the info of where you will stay
I've done what you want to do, your WP needs to be cancelled and you need a letter from your company saying you have left. You have 7 days to reapply for you Thai wife ext. The money does not need to come from abroad, but should be in the bank 2 months at the date you apply. Best to check with your local immigration office what else is needed as it can vary.
The "smart" transfer system is a Thai domestic system, regardless of how it's sent if it goes through this system onward to another bank it will be as domestic payment. Not all transferwise payments go this route some go direct, and in this case they are seen as international transfers in the receiving bank. What makes you think the system has been changed?