You are often constricted by where the exit/soil stack has to go, so some of this might not be feasible.
Get a toilet that is completely smooth with no little details that trap dust (and worse) - if the walls allow for it, a hanging one so you just swoosh a mop underneath. And a self closing lid.
Dual fill flushes are rubbish. Really, really rubbish and invariably start initially trickling and then pissing out water constantly within a short time, which costs a fortune in water.
If you can afford it, get either a bidet style toilet or ensure you can connect a separate mini shower head to a thermostatic mixer for warm water for intimate washing.
Get as large a sink (again, if possible, a hanging rather than pedestal) as possible. One with an inbuilt vanity can be very convenient.
The other thing that really annoys me is when the only place for a mirror is on the windowsill directly behind the sink. A cabinet on another wall that includes light and power for toothbrushes and shavers (have more than one) works far better.
I'd say that the best heating is underfloor, as towel rails don't do the job well.
I'd have bath behind the door, toilet on the adjoining wall, sink under the window, then shower and decent mirror cabinet on the return towards the door again, depending upon how wide the window actually is.
Wet rooms are rubbish. Never have one unless you absolutely have to for medical reasons - a level, sealed, large cubicle is miles better than an entire floor swimming in water.
Oh, and floor to ceiling tiles make life so much easier.