I would definitely recommend you buy a lighter coloured sofa, perhaps a couple of occasional chairs, introducing some texture/colour. Some complimentary cushions will tie it all together. Use a rug (big enough to go under the sofas/chairs) to define the space and replace coffee table with a smaller more refined one, or a set of two nesting. I would also change the dining chairs, with something lighter in colour and not as high. Enjoy!

Looking at your proposed changes to kitchen floor plan, and if I'm interpreting it correctly, I think having the cooktop in LH corner of long sink benchtop would be somewhat awkward & hazardous esp having an opening/door into the room right there. I think there needs to be adequate space on BOTH sides of cooktop to allow more elbow room for cooking processes, setting hot pans/pots down, etc., and also need to think more about opening/door placement in this scenario. Will you be replacing the current sink? If so will you have a single or double and with or without drain board? Do you want dishwasher to right or left of sink? Would be good idea to include Euro bins in new cabinetry, and as many drawers as budget will allow. Maybe can include a spice drawer? does your current pantry function well as is?

Looks like you have a corner block and north is at the front. I would ditch the void over the front door as it creates constraint upstairs for limited benefit given it’s small size. The alfresco is my biggest concern. It seems too small and will be impacted by western sun in the afternoons when you want to dine making it even smaller if you have to screen off the sun. Living would be better on the west than the kitchen too. So have a look at how you would use that space. Can’t see eaves but really important to protect kids bedroom from western sun too. Limiting window helps and using external Louvres are some techniques. Is it possible to get a design that links to the garage?

I would re-evaluate my brief, my budget and my site. It is another case of trying to squeeze too many rooms into too small a space and compromising the living space. If you draw furniture to scale in your living room then you will see that it is undersized for a four bedroom home. With the best orientation going to the garage door and bedroom 4 I would look at a complete redesign by pushing some of the bedrooms to the rear, and a central courtyard to give you an opportunity for north facing light to a living room. There is nothing nice about the current design and will feel like an apartment with little resale appeal. The designer has shown no flair or imagination in this "gun-barrel" floorplan, and is a variation on a concept that has been around for centuries. But your biggest problem is the number of rooms. Do you really need 4 bedrooms plus a study and 2.5 bathrooms, a long wasteful hallway, and only one modestly sized open plan living area and kitchen on a narrow block? I would start again with a smaller brief and a designer who can challenge your thinking about what good small house design actually means. Small house design is the hardest to do really well, so don't use a large house designer. Dr Retro of Dr Retro House Calls and Dr Retro Virtual Visits