the work permit itself, once you have a job, and the paperwork from the company, is bt3800. But understand that if you aren't fluent in speaking and understanding Thai, Laotian, and Burmese, you aren't qualified.
depending on the type of business, and setting it up under the BOI, the owner, no matter what country he/she is from can own 100%, and only has to have at least one Thai employee, and can even be part time, as every business must have a licensed Thai accountant, with no exceptions, except for occasional internal audits.
Yes, by all means use a lawyer. If for nothing else you will need one at least to professionally draw up your articles of incorporation, and stockholder bylaws. Siam-Legal.com is very good. You can not work doing business in Thailand on a DTV. Also, a type O visa extension based on Thai wife allows you to work, without needing a type B extension. This takes away any threats an employer can make concerning losing your right to be here if you get fired.
When you initially apply for your type O 90 day visa based on retirement on the e-visa system in the US yes it does work, but after you arrive in Thailand on that 90 day visa you must get a Thai bank account and put the bt800,000 in it at least two full months before you apply for your one year extension of stay. The US embassy no longer issues wage statements so you must use the bulk sum method for your first year extension. There are no exceptions to this. By getting your type O 90 day visa before you arrive in Thailand it makes it very easy to get your required Thai bank account once you get here
A written letter is required from your employer, or your own company, stating that you are allowed to work remotely. Another thing that is lots of times asked for from self-employed person's is your most recent income tax filing.