Option 1 is fine but you have no vanity space and these tend to look poky in smaller bathrooms. This is a smaller bathroom, this can be eliminated with say frosted glass walls. But you are changing a bathroom for one that is similar sized, worst case mirror the WC over so it gets some ventilation. Option 2 are you kidding me a full length window in the shower? where is the entry to the master? is it coming off the living room? Option 2 good use of the hall, but the planning of a free standing bath in this small main bathroom will make it appeal smaller is there no shower in this option? If you are going to the expense of making wall changes, what about taking the bath out to the eaves, if you have them which will give you 600 mm more space? If the master is coming off the living room? If the overall internal dimension is 4.2 M and you need say 900 mm for entry to ensuite and 100 mm walls, that leaves you with 3.2 M for ensuite. Looks like you are taking out lots of walls, so to me if you changed the access to the WIR and ensuite to the other side, the vanity can be near the full length window, which solves the water issues of it being in a shower, and it would be nice to be pushed out the 600 mm like the bathroom, and if you were willing to give up say 300 mm of space from the bedroom side, 4.2 x 3.1 than you could have hanging space (which goes into that proposed new access point), on two sides and then a total wall of storage in shelves or drawers or places to put shoes and bags and ties and smalls on the ensuite side.

keep in mind that my plan has single external walls and all the inside and outside walls are 10cm thick to make drawing easier and the depth of the verandahs includes the eaves, adding a brick veneer would use more space and given the choice it would be lovely to plan for a covered walkway and raked ceilings in the living areas and this is a very basic gable roof but there are lots of more exciting/expensive roof options to consider

No, builder coming around tomorrow for first time, as is Class 2 designer (been a rush to get a bunch of class 2 consultants on board for a simple reno). So far all my own investigations. The slab is structural, 275 thick with localised thickened beams over the posts in the carpark. Opening it up would probably be refused by Strata. I can go look at the original structural details to see how much cover is over the reo - maybe I can get a 20-30mm scabble and do the rest with screed to cover before tiles. It'd be very flat though. Will need a structural engineer to sign off on the detail, and if I'm honest, I'm uncomfortable reducing cover to the reinforcement as below and think it opens up a bunch of risks. I'll run this past them tomorrow for their comment though.

Hi Kate, I'm yet to measure it up or see if any tiles are under vanity (settling next week). The property has an outdoor laundry (under the house) but would like to have this inside. Thinking if the washer/dryer is more centrally located (rather than in corner) it might be OK. Hopefully it can be done.