Help with T&G panelling/skirting/floor tile interface behind bath

[globalste1]

I’m going to be putting T&G style (water resist mdf) panelling against a half stud wall (possibly use something like aqua board) which will have enough space to run the pipe work for a freestanding slipper bath taps (wall mounted) and handheld shower attachment. The panelling is 1200mm tall and will have a rebated dado rail sitting on top. This will be the height of the stud wall.

I want to make sure this is all as waterproof as possible as my fear is kids spilling water over the edge of the roll top freestanding bath, so I was thinking about tanking the stud as though it was a shower, but what I’m not sure is what do I do first. My thought was:

1. tank and seal the stud down to the floor (considering using something like hardie board)
2. Tile the floor
3. Fit the panelling
4. Fit the skirting
5. Fit the dado rail
6. seal everything
7. Prime, Undercoat and paint the panelling and skirting board.

I’m unsure of the best way to make the join on top between the back of the dado rail on the front of the stud and the depth of the stud back to the brick wall (like a mini shelf if you will), is wood ok with this providing it’s primed and painted and sealed or should I use some pvcu or even small tiles? any help and ideas are warmly welcomed.