Tumbled marble might look out of place if it's the only natural texture in the room. If you want to keep a similar contemporary mosaic, then 2 things for you; Firstly, measure for yourself the actual mosaic sheet - don't take the written dimensions as gospel. Secondly, once you have a couple of favourites in mind, take a look at tile trims to incorporate with the mosaic. Remember, you can cut the mosaic sheets into thinner strips. Trim could be square edge tube style trims or even L shape angle in either aluminium or chrome and can be used at the sides of your mosaic or, in the case of the angle trim, used in multiple vertical lines running through the mosaic. Knowing the dimensions you have to play with will make it easier to design a solution that keeps grout width to appropriate size of 2-3mm for wall tiles.

subject to correct measurements, your idea of moving the laundry sounds good but do you really need the expense of installing a side door...why not continue taking the washing out through the doors to the deck, accessing the laundry through the kitchen doesn't need to affect the entry and instead of joining the study with the old master bedroom, why not include the study and back bedroom and ens for a new master suite with the best view and by relocating the toilet, opening up some internal walls and a new kitchen layout you could achieve the open feeling you're after ...but only correct measurements will confirm the possibilities especially info about the block, roof and walls

Think of recessing the Mirrored shaving cabinets as being recessed the same as the Niches in the shower wall, simply they remove/cut out the plaster board to the size/position and shape and frame that up with timber. The plaster board on the back of the recess belongs to the room behind and is the wall for that room, so makes no difference to your WIR. Just a thought if you go for the recessed wall cistern, when my brother inlaw did theirs the Architect suggested that they have a discreet panel screwed back over it, not fixed and plastered so that if any problems developed, Leaks etc it would be easy to access cheers

Yes keep the bath. 99% of my clients still request a separate bath. My wife and daughter still use one. Young kids still love a bath. I would look further into relocating the return air for ducted. Its not really central to the house anyway so could be underperforming. Probably easier to relocate it as this can open up opportunities for better bathroom layout. Whats in the space between laundry and kitchen, looks like a wasted area that could allow a bigger laundry, linen cupboard with space for return air.... 2480 x 1800 is plenty of room for the smaller bathroom. Allow 900 for shower, 900 for toilet and 900 for a vanity. Lot of layouts that you could try. Use a 720 door if need be. 2480 x 1800 for the other bathroom would be say 900 shower with a 1500 bath. Relocating return air and adjusting the door location and the walls would allow a reasonable bathroom layout and more layouts and a bigger bath. Note: door location is critical to the layout and not overly expensive to change compared to the money spent on rest of bathroom.