As surprising as it may seem, starting the business on a tourist visa is more common with the extensive aid of an Accountant who has a working relationship with a lawyer (for certain documentation). Then it is common to hire a visa agent to apply for your Work Permit and B Visa. These two credentials are intertwined and the applications must be done in proper sequence. I suggest budgeting from 45 to 65 thousand baht for the process. This can be done a bit differently and a bit cheaper but for newbies - I recommend my way.
The ability for Foreign Employees having a B Visa and WP to get the 12 Month Multi-Entry B Visa has been cut off... Forcing their employers to get them an Extension of Stay instead and that will mean having to report the Thai / Farang employee ratio with Social Security Tax and Income Tax withholding tax. Next likely no 12 month multi-entry B Visa for Directors - just a matter of time.