From your drawings I leaned towards squaring off the arches but seeing the house IRL I say keep them. Being raised from the road and the way the house is perceived to sit into the land, they look great. There is a graciousness to the arches which you don't often see in houses of this era, I think it because they are not uniform. I would look at the Spanish Mission style homes in Palm Springs for inspiration and keep the roof tiles rather than go colourbond too. You can still do a version of beach just more Spanish mission hacienda style!

i put the bathroom next to the master to have the bathroom door off the short hallway rather than opening into the retreat and if you draw a line across the floor in your original plans to make a path where you will walk and leave space for furniture you will see that despite the size of the retreat it was just like a big hallway with no where for comfortable furniture arrangements and i would double check with the Solar panel supplier to confirm the ideal roof angle... double glazed windows (or thermal break double glazed are better but much more expensive) but windows can't exclude the worst of the summer heat without external window coverings and big areas of east and west glass will impact your compulsory BASIX ratings and playpens and baby gates across the top and bottom of the stairs makes everyone safer and also useful to keep small kids out of open plan kitchens

I have to agree that Builders don't like any big changes and will apply extra charges to do so. I suggest the following small changes. i) The fridge needs to be swapped with the cook top, the pantry looks like you can make it longer to line up with the outer edge of the island. Is the island 900 deep to allow you to sit up to? Have one of the newer deeper squared sinks preferably with 1 1/2 tubs to hide dishes in 2) The laundry, don't go with a sliding door they are a waste of space, and won't allow the bench to go full length, instead a small window at the end and above the bench which shoud have the sink below it. plus a a glass hinged door. (check our some of the display home with the sliding doors!!) Plus add a doorway from the passage 3) Try for wider wardrobes in the bedrooms with sliders for more space 4) Maybe add a wide Barn door across the opening into the family bath, bedrooms 5) Swing the garage door inwards, if the garage is deep enough step the door in from the corner to allow for storage along that back wall.

The wow factor can be achieved in many ways. You have a big parcel of land at 700sqm. At the moment you have a big box as your house plan with, in my opinion, too many rooms for only 3 occupants. You obviously have a decent budget, so look at a plan that has multifunctional rooms, that will offer the same use but not vacant rooms not being used. You have 5 bedrooms and 3 bathrooms and 4 living areas, for 3 people. Do you have a view, will you ever actually sit at the balcony or just have to sweep it when dust accumulates. Build smart not necessarily big. Are you needing a house with all these rooms, or are you trying to impress friends and family. We all want to impress our friends and family, but a nice looking home with a wonderful FEEL and the WOW factor doesn’t have to be lots of rooms that may not get used.