Your main decisions
A like-for-like layout can simplify a renovation. Moving a WC or shower may change the drainage route, floor build-up and amount of making good.
A walk-in shower needs space, a suitable waterproofing system and a workable waste route. Tiles and grout alone should not be treated as the waterproofing design.
Concealed cisterns and wall-hung fittings create a clean appearance, but support frames and service access need planning before the walls are closed.