A remodeler will look at the floor framing, the drain location, and whether the bathroom sits over a basement, a garage, or a finished room. With a median Bridgewater home built around 1984, the bathroom floor is often sheathing over wood joists, and recessing it for a curbless entry can mean adjusting the framing rather than just the surface.
Permits come through the town's online system, and the Building Department, which includes the plumbing and gas inspector, enforces the codes that apply. Nothing should be torn out until the permit card is in hand. The plumber's rough work gets inspected before the walls close, and the new pan should hold standing water in a flood test before any tile goes on.
The usual order is demolition, rough plumbing, waterproofing, tile, and then glass, which is typically measured after the tile is set and installed later. Ask about the glass lead time early so the shower doesn't sit finished but unusable while you wait.