There are dedicated house removal people who could take it off you, I don't know if they charge or pay for that. Demolition services may also do something similar. Googling house removal melbourne there are a few listed. Here is an example. http://www.khr.com.au/selling/ Another option would be just to list on gumtree or the paper and offer for someone to take the house. Either selling or giving away whoever wants the house organises the removal. We got a house like that... the owner of the land wanted the house gone but didn't want to pay for demolition, we wanted the house, we payed for the uplift and it was win win.

I definitely agree that once you live in a home for a few months you will have a good idea of what works and what doesn't. Assuming that the large room with the floorboards is the living space and the room with the slate is the family room, would it work if you knocked out the wall between the kitchen and the family room, rather than just having a pass-through? You could then leave the fireplace wall alone and put a bank of fridge, pantry and wall oven(s) on the kitchen side. You can have a large return (peninsular) between the side walls. This way you have a very open view into the family room where your children will probably spend a lot of time and you get to keep the fireplace or some version of it. If the rooms will not be used in this way, you would be better to remove the fireplace and the wall - but only if you can find another wall in the kitchen to relocate the fridge, etc. From a design perspective, while the kitchen is dated the timber can be painted and new knobs or handles added. You can have the benchtop resurfaced and a new splashback possibly installed over the existing one. However new kitchens would have more drawers than doors. If there was detailing on these it is more commonly a very simple Shaker profile that suits the very popular Hamptons style. Otherwise they are plain with shadowline or push to open. My advice would be to live with it for a while and then as soon as your budget allows get a new kitchen as part of the bigger renovation.

the space size will/should be determined by your furniture layout and size. For example if you have a round table of a certain size vs a rectangular table this will change what is required. Same with lounge furniture. With living room it becomes more involved depending upon whether you have a fireplace and a TV set up as the lounge furniture needs to be able to work to both. If you want a more formal 3 piece lounge setup vs a more contemporary modular corner lounge with chaise end then this will change room proportion, TV/fire positioning and also paths of movement around/through and into the space. Your issue with the dining space is more about the bottleneck in and out of it The size is just OK (with update plan) although if you have a 2.4m length table you best have closer to 5 or 5.5m length to have comfortable space to move around the table ends if people are seated at the ends. If your living and dining areas are more combined then overall you may not need to increase the size of the building, rather you have a more efficiently planned space as you can "share" the swing room around furniture to a certain degree. However you may prefer the separated configuration, which is fine, but it needs to be set-up with proper clearances around both the built in and freestanding elements to function well. Have attached an example of one of our projects, a completely different thing but inspired by a traditional style - the plan however shows how the spaces are designed specifically to furniture and paths of movement is flowing and balanced with no awkward bottlenecks in this regard. Also the more centralised living zone enables a more efficient relationship between entry and main living.

you've almost finished your home owner building and had a new baby during Covid...what an achievement, congratulations..i would phone the building inspector and ask if you can add the cavity sliding doors before you move in BUT if the inspector implies some long delays then leave the new opening until after you move in ...