You don't need a workpermit if you're working for the company you own, however you still cannot work in a restricted field.
Example is a foriegn resrurant owner doesn't need a workpermit to cook the food in his restaurant, but he cannot deliver the food because anything related to transportation is a restricted field.
I just don't understand how you'd have PR and think you'd need a tourist visa to enter then. The answer to that question would be no, PR holders don't need anything to enter Thailand.