Just a thought, have you checked your lovely flooring will persist under new cabinets or more importantly the gap created by the island bench. Possibly put a simple narrow breakfast bar (with power point of course) across a couple of the window sections, lovely to sit and look out of the window and preserve the look and the light. Then you would save some depth into the living space, as the current breakfast bar is quite large and deep.

I have high ceilings downstairs 2.7m and std door and window height and looks fine but do have wider front door 870mm don't like tall and skinny doors. Having said that on one wall do have higher windows and they look fantastic but that was to catch sun and block out ugly neighbour house so std window size just fitted higher but look so good in my downstairs open plan area could have gone larger height windows all around but don't have verandah across front house that would look odd with higher windows and no light benefit and more heat n cold thru glazing. Good luck with your decisions

This wasn't your question, but looking at a possible boxed out window in the open plan kitchen dining living it shows just how limited you space is. The following 3D overview shows a boxed out window seat. I have run the kitchen along the same wall as the new window, The Island is 2m x 900 with 1m between the wall base cabinets and the island and 1m between the Island and the wall where your plan shows cabinets. If you have/had cabinets along the other wall as shown on your floor plan they will be 600 deep this would make the island 1400 x 900 which is small. Has your kitchen been renovated and were you considering that, if not. Looking at the overall size of your open plan area I would be considering 1 or 2 large stacker doors to open up to the rear alfresco, that's what I would do but you need to choose what will work for you PS I think that the boxed out window at the front of the house is a lovely idea but possibly not right when it faces West.

Agree with Siriuskey above. Hard to decide without seeing the style and layout of the house. If the expense of 3m windows is prohibitive, stick with the 2.7m ones and go for the 3m ceilings in the larger spaces. Install curtains at ceiling height so when drawn, it has the perception of full height windows and gives you nice simple lines. See below. Smaller spaces like powder rooms and studies perhaps you could have lower ceilings but that doesn't always save any money but small tall spaces need to be treated differently with the decor. Also heating in winter in Melbourne will have an impact on your energy bills. Heat rises so having low down heat like in slab heating will make the space more comfortable for the dollar spent. Think about fans in winter to bring the heat back down as well as for cooling in summer. Are all the downstairs spaces flat ceilings? I.e, no double height or sloping ceiling spaces? The amount of light in a space doesn't only depend on how high the windows are. Sun shines downward and so having windows go down to the floor and spread across floors may have more impact on light levels. This depends on where you place furnishings, what floor coverings you have etc. In bedrooms for instance where there may not be great views and you want to maintain privacy, I often prefer to have narrow tall windows carefully placed rather than the typical developer wide high sill windows centrally located on the outside wall. Are you on a suburban or urban site of in the country? That will impact privacy vs views. How much overhang or screening will you have to prevent summer overheating? If someone is designing this house for you, they should deal with all these issues with you. My feeling is there is much more complexity to consider than just your one query. Share your plan and elevations for us to help you more, even if they are just sketches. Good luck, C.