A remodeler's first visit usually covers the floor framing, the drain's route to the building sewer, and, if there's a basement under the bathroom, a look at the joists from below. For a curbless entry the floor has to drop or be built up so it slopes to the drain, and that's easier to judge from underneath. If you want more than one outlet, expect the plumber to ask about the well pump and pressure tank.
Lakeville's Building Department enforces the building, plumbing, and electrical codes, and permits are filed online through the town's Viewpoint system. The plumber files for the valve and drain work, and an electrician files if the job adds lighting, an exhaust fan, or a heated floor. Ask for the rough plumbing to be inspected and the waterproofed pan to be flood-tested before any tile covers it.
Many Lakeville houses have one full bath. If yours does, settle in writing how long the shower will be out of service and whether a temporary arrangement is possible.