Waterproofing needed for cement backerboard? - Tile Advice

[Topcad]

Hiya all,
I'm a DIY gal on first bathroom. Wondered if you could check out my plans and let me know how I'm doing?

Walls
15cm x 15 cm ceramic tiles
Plastered masonry and plasterboard with Hardiebacker 6mm screwed on top
My bf got normal plasterboard rather than water resistant so I've waterproofed it with Mapei shower waterproofing kit
Will use BAL whitestar adhesive

Floors
Original floorboards
12mm ply
BAL White star adhesive between ply and backerboard and backerboard and tiles
Hardiebacker 6mm
porcelain mosaic tiles

1. Does the hardiebacker need waterproofing around shower area and floor? I have lots of Mapegum WPS left over from the waterproofing kit but just want to check it won't affect the bond between adhesive and backerboard

2. or should I use 100% waterproof boards around shower instead of cement boards? If so which do you recommend? Is Marmox multiboard suitable.
Need to use cement boards on floor as they're stronger

3. Should I prime the ply? what product is best?

Any other recommendations?

Cheers!

 

[Topcad]

Just to clarify it’s a bath with shower above not a wet room