Been doing bathrooms for years — a few practical bits from the builder side before you lock the layout.
Toilet: keep it as close to the soil stack as you can (front right in your plan). Every bend and extra run of pipework is a future blockage risk, and Building Control will want proper falls. Moving it a long way usually means boxing or a macerator, which I'd avoid if you can.
Wetroom / tiled walk-in near the door: that needs a proper tanking system and a fall to a drain (usually about 1:80–1:100). On a timber floor it's doable but more fiddly (tray former or screed + membrane). Make sure whoever quotes it is clear about the waterproofing product and that it's continuous up the walls, not just a tray.
Freestanding bath under the window: fine, but put the trap/access where you can get to it without ripping tiles, and check the window board height so you're not leaning over the bath to open it. Also think about splash — a freestanding tub under a window often wants a good seal at the sill or a sill tray.
Half wall to hide the loo: useful, but leave space for cistern access (or use a concealed cistern with a service hatch). Electrics in the wet zone need to be Zone-compliant (extractor, lights, heated rail) — your electrician will set that, just don't put sockets in the wrong place.
Ventilation matters more than people think once it's a wetroom. An extractor that actually vents outside (not into the loft) will save you condensation grief later.
Get two or three quotes that break out plumbing, waterproofing, tiling and electrics separately so you can compare like for like.