I am just looking at the conditions of a 'permanent Resident Visa'. One condition is that you must hand in 3 years worth of tax statements.
So is the inference that you must be on a business visa for three years in Thailand to even think about the permanent resident visa?
I'd love some clarification if you can shine a light!
TLDR : Answer Summary
To apply for a Permanent Resident Visa in Thailand, you need to have three consecutive years of extensions of stay based on either employment or marriage, not just a business visa. This means staying legally in Thailand for three years, along with maintaining a minimum salary of 80,000 baht per month or having a capital of 10 million baht in a limited company as a shareholder. Language proficiency is not required for the permanent residency application, though it may be a factor for Thai nationality.