I need to consider my approach. I am also down as Principle Consultant at my pals Pharma Consultant in Singapore. He has not done any business yet either though.
I would not be thinking too much about the Thai Tax situation at the moment. Even if in Thailand and tax resident in 2025 tax submission not due to till March 2026. Wait and see how it pans out for those on O visas. Even if yiu are Thai Tax Resident only monies remitted to Thailand are assessable. The UK also has a double taxation treaty with Thailand - read that. So lets say you earned in UK and were taxed on it in UK. Depending how much you remitted to Thailand you may owe some Tax here depending on allowances, and tax rate differentials. Unless you are planning to bring in a lot of money I would not worry. If you are bringing in large amounts consult an international tax consultant.
Let's see how this develops. The DTV is 6 months old. Already in 2025 we have seen more scrutiny and posts about it. It seems to be mostly those with "Complicated Immigration History" ie back to back tourist visa, border runs, Ed visas. It really is too early to make definitive predictions. It has been made very clear by a senior MFA official in the FFCT interview and it is clear on the MFA website it is Immigration who have final say on entry and extension