Forming the business will take a lot more than a "business license" and a tax file. Thai Registered Companies require considerable documentation starting with the Company Certificate with the detail of share ownership, designation of Director(s), usually 2 Thai Partners having 51% of the shares.
Americans are exempt of Thai Partners if the Company is formed under the Treaty of Amenty. Board of Investment Companies have different rules. A BOI knowledgable person will have to explain.
Regardless of other factors the uncle will have to be in Thailand on at least a Tourist Visa to have enough time to deal with the lawyers, accountants and government bureaus
I tgought every B Visa Application had to have an WP.1 / WP.3 / WP.x marked as having been received by the Labor Ministry and an official Labor Ministry letter saying same
Also a for a shareholder - Farang or Thai - he or she does not automatically become a Director. A Director has to be appointed by a majority percent shareholders. A Director is the only shareholder who can make decisions - sign contracts, make tax filings, sign financial reports or create bank accounts, etc. In my opinion I do see any Company assigning a 20% shareholder as a Director.