check with a Thai accountant but what I have been told: any amount withdrawn from an ATM over 4k per year, you owe Thai tax. If your home country has a treaty, then that amount paid to Thailand is deducted from USA etc. tax due.
Too many applicants had "loans" from parents of the 500kb for a few months. Makes sense to crack down on this. We don't need DTVers going freelance on Bangla for income and competing with local talent!