depends on the kind of visa. My non-B was convoluted with work permit, visa, suspending the corp, final accounting, and commercial rental space. Other visas you probably just go to immigration and done.
Today I stamped in with DTV for 6 months. They saw the re-entry permit, dug deeper, saw b visa. Some discussion with supervisor. I told them I will cancel b visa asap and they seemed happy with that.
Not really. You need business registration from your city/state, tax return showing income schedule for that business, etc. Coverletter should say "no Thai clients" if that is possible. Tax bills, etc.
If stuff is in the business name, include paperwork that shows you own that business. Everything must lead back to you personally.