Please don't be worried. My wet room floor problems arose in a new build extension - concrete floor, then screeded to provide the correct gradients - not! Your project has a custom-made floor base with a built-in gradient, which should over-come these problems. McAlpine seem to have excellent range of traps etc.
As a self-confessed spirit level freak myself, I even put the toilet door lock on using a spirit level. I sit there each day and fret because it's not level!
Regarding the tiles, would suggest wall tile overhangs floor tiles to preclude any possibility of water ingress if seal between wall and floor is not 100%. But appreciate problem of batten/tanking.
I posted photos as a reply to an earlier project -"En Suite, Now With Added Dimensions, March 2008", which shows tiling, floor and drain. (Can't do those clever links.)
As a self-confessed spirit level freak myself, I even put the toilet door lock on using a spirit level. I sit there each day and fret because it's not level!
Regarding the tiles, would suggest wall tile overhangs floor tiles to preclude any possibility of water ingress if seal between wall and floor is not 100%. But appreciate problem of batten/tanking.
I posted photos as a reply to an earlier project -"En Suite, Now With Added Dimensions, March 2008", which shows tiling, floor and drain. (Can't do those clever links.)