Maybe this will be helpful: "Ergo then... to meet the principal-place-of-business qualification one must have an office at home?"

You would Not have the first trip or part of the trip as being From the office, but from Home, unless Home has a Home Office. The principal place of business is a Place. It isn't by definition the Home, unless it meets the requirements as defined. The principal place of business might be an office downtown, for instance.