Fitting fibre sheet to shower wall (hole)

Hoping someone has a brilliant idea. Shower in IP developed a leak behind wall. Turned out to be the breeching piece behind the taps. Plumber has fixed but now a sizable hole in the wall (i'd post pics but wife's out with camera).

The hole is 400mm x 300 mm (4 tiles) and taps are in middle of hole. Taps are fixed to timber noggin behind. I wave a wall stud down one side but nowhere else to fix the board to.
Firstly, can I use standard fibre cement sheet or do I need the aqua stuff?
Secondly, I can nail the villaboard to the wall stud and thinking of using an offcut of villaboard to sit behind sheet using liquid nails.
Thirdly, after I've tidyed up the hole and fitted the sheet, how do I fill the gaps around the sheet to waterproof it prior to tiling?

Any advice is appreciated.

Project 1080


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