It is probably a bit narrow for a theatre room. The area that will let it down is from a sound perspective. Placement of speakers is crucial to getting the effect of surround sound. Putting it very simply, too close together and the sound will blend in together. Too far apart and you will get a dead spot. If they're not angled appropriately you will get phasing issues which will cancel out certain sounds. For that depth of room, i would probably recommend about 4.5m wide. On a slightly different not, i find the placement of the laundry rather odd. You will get the noise and vibrations from a washing machine/dryer in the two rooms that you probably least want it in. The other consideration you may want to look at is keeping the rooms that have plumbing on the same side of the house or at least as close together as practical. Keeps building costs down.

Thanks oklouise for taking the survey, we're looking forward to sharing the findings with you and the Houzz community. Not compulsory for you to say so in the comments! Happy for everyone to remain completely anonymous :)

Can I suggest you consult with a building company, for example Summit homes in Perth. They build project to high spec homes and have their own design team. Therefore have bulk buying power for build products. They also offer knock down rebuild services. You have been very indecisive over the last 18 months when planning your huge renovation. So dealing with a company that knows your land and council regulations would be beneficial. They can start with the things you know you require and with your consultation design the rest. You can deal with one design team and be focused on your build. This Houzz forum is great, but in your situation I think you need someone to help you through the design process personally, who can walk on your land. They also offer full home renovations......

In Victoria our planning scheme has min dimensions for rooms in apartments and for garages. Single garage 3.5x6m. Bedroom 3x3,6m includes space for robes. Aim for 2 living spaces or a bedroom that can be second living space in a large house. The current trend for open plan kitchen dining family has everyone in one space which can be noisy and intrusive if no other space available. Toilets. Large family house needs 2 toilets all can use. Burying one away on ensuite results in need for a third Do a furniture plan for dining a family including storage. I find drawing up all items to scale cutting them out an placing on plan the easiest way to look at options. Include your fireplace as a cut out. You need to be able to accommodate everyone. Tv? I suggest talking directly to an architect to refine your plan. A house is a major investment so cost of architect justified. Also look at volume builders plans on internet and go see their display homes