Depends on individual circumstances, but it's all there is the DTAs on the TRO website. In my own individual case (and I'm sure there's others in similar situations) I'm a dual tax resident (have been for years - many people believe the 180 day rule is something new, which it most certainly isn't), but due to the tie-breaker contained within my home country's DTA, I retain full tax residency in my home country, which is further backed up by the conditions that my pension is only taxable in the country of residency, which is my home country. I've been in Thailand for 15 years and looked into this years ago, and have never required a tax ID or a tax return as I have the certificate of tax residency from my home country. Naturally those that have severed all ties with their home country might be in a different position, but there's certainly no blanket rule
You do nothing. There are fear mongers out there who actually believe Thailand will tax savings. They cannot get it into their thick heads it's only possible to tax UNTAXED INCOME.
Genuine feedback? What do expect to pay for a guaranteed five year visa? You really believe a cooking course will cost that much in Thailand? Still, I see you are choosing to live in that Godforsaken wilderness called Isaan. That speaks volumes! π
It's perfectly legal for you to have two passports, even from the same country. You use the one with the Thai visa to enter and leave Thailand, and the other one to show when checking in for your flight