To change to cavity doors you will need to remove the wall each side of the doors to accommodate the cavity housing. Normal sliding doors would make a difference but the problem with them is they never stay totally closed and they do become quite noisy and annoying. This problem also applies to double cavity doors. The other option is to use bi-fold doors, they won't intrude into the room as much. Do you really need two doors there at all and is the glass above the doorway necessary? My personal preference would be to fill it all in and just have the one door to the room. You could even re-use one of your doors.

If your block is facing North or West (within Australia) maintenance will be required to ensure movement is minimized. Timber doors are beautiful they just tend to be susceptible to sun damage. FYI Cutek is a great timber protector if you want to keep the natural look however you will need to keep applying year after year.

if you decide to have a wall hung toilet or towel rails on the toilet wall the cavity slider wall will need to be reinforced to support the weight and a wall hung toiler with inwall cistern will mean that the cavity slider would have to slide towards the vanity..Either hinged or cavity slider doors will be good in this situation although the hinged door has the useful option for hooks for clothes or an extra towel rail...btw consider moving the master bedroom entry door for a more generous entry into the bedroom

It would not look odd and is quite common. I've sold many robes over the years that had shaker-profiled sliding doors. I would highly recommend a heavy duty track like the "Indaux" system Nover sells and use 18mm doors.