Certain items such as tiles , doors and window frames have long lead times and are one of the first items required on site. Also your chosen bathroom fixtures and fittings may need to be ordered from over east. The plumbers will need a list of intended fixtures and fittings even if they are not in stock. Keep in mind the plumbing prelay is one of the first items to go in the ground.
Make a decision regarding floor grates in the bathroom. A common mistake is not to provide a location on the drawings in which case the plumber will put them where it is most convenient, ie.in the middle of the room. This is located even before the ground floor slab is poured.
Floor finishes if not stated on the drawings need to be selected before work commences on site as this affects the height of the slab.
Even if council will send your plans to your neighbours for comment, and you’re not legally required to inform them yourself, you should still have a friendly chat over the fence. Your neighbours may have very valid concerns, and if you’re aware of them before you submit your plans or start work, they’re far less likely to delay construction.