Given your vanity choice and tile choices, you look like you favour a transitional style. The dado height suits this well. We've done similar in 2 of our bathrooms. It would be lower (1.2m) than your existing tiling around the bath.

depending on the size of the existing vanity it should be possible to have a similar new vanity or a custom unit made to replace the original but a chat with a plumber should be arranged to recommend suitable options and plan a schedule to remove the old and install the new, including any necessary waterproofing or tile repairs..btw careful removal could allow the original sink, taps and even the counter to be saved and recycled into a new vanity that matches the bathroom perfectly with the added option of being able to add different doors or drawers to the cabinet

Have been double waterproofing for many years and NEVER had a bathroom leak Have renovated many 100 yr old bathrooms 1..... Remove floorboards, check dimensions ,spacing and condition of bearers and joists and if level...More often than not 100 yr old homes do not meet 2020 Standards And all supporting timbers require replacement ( Not a big job, worth the effort ) 2....Plumber should check drainage, moving items easy and cheaper at this stage 2 ....Lower if necessary to level timbers and Scyon to finish 40 mm lower than outside floor, fix to manufacturers spec 3... Plumber to fit item pipes and drainage penetrations ( Puddle Flange ) consider location of floor waste ...may be preferable under vanity drainage for shower and floor waste.. 4....Waterproof entire floor, up walls 300mm shower etc to standards Prime and we use Davco K10 plus, 5... Add water bars to shower and doorway, Sikaflex , adhesive/sealant ( NEVER Silicane ) ALL Walls to floor.' Shower corners to 2000 mm Waterproof second coat 6...Tiler to lay tile bed and establish fall to floor and shower 7.. After drying, Polyester bandage shower walls to floor, Waterproof Third Coat 8... Final Coat of waterproofing 9...Tiler to tile Ii takes around 7 days to waterproof as for $ 50,000 bathrooms Any further questions, Pleas feel free,If in Sydney Contact

I would prefer to keep the WC separate to the Bathroom as you have 3-4 kids? who will get bigger very quickly, having a powder room downstairs won't help with the morning rush to school., But it's your house so I have added a pocket door between the WC and Bathroom. I have also taken that small robe space for an extra vanity in the WC/Powder room. No width dimesion given for the WC The ensuite could use that extra entrance space as a sit down makeup and hair bench for your wife.