realising that you did not mean to have one long narrow room but i think we all recommend an L shaped extension (not necessarily my suggested plan) because it will be much more cost effective than removing the whole back wall of the house and replacing all the separate ceilings and windows and not achieving much more than an enlarged bathroom, bedroom and small ensuite..the Lshape extension of similar sq m would create a more comfortable floorplan for the whole house with a simpler extension that also has the potential for a deck or alfesco to enjoy the bush view..photos of the roof and back of the house and measurements of the distance to the side and back fences and location of the pipes you mentioned and rough measurements of the bathroom, laundry, wardrobes and short hallways would allow a much more detailed floorplan to help invite more suggestions

This floor plan has a single garage, with bedrooms grouped together at the front of the house, the Music Room has been moved to the rear away from the bedrooms as it would make too much noise for those sleeping. It can now be opened up to the family kitchen dining, courtyard and Alfresco and can be used as a play room(/ guest room) giving children great indoor out door play area in view of parents. There's a study with a similar view. A powder room closer to the rear of the house for easy access, The main bathroom is done Japanese style. The master suite has the WIR between the bed and the ensuite, no noise etc when in use to disturb anyone. I have made the passage way extra wide and more like a room which has a linen cupboard, you could certainly make this narrower and add to the bedrooms if you wished, This comes to 204.5 sq m. cheers

the two plans are close to the same size different arrangemts make some room bigger in each plan but what does your builder say?? plan 2 has a bigger alfresco, bedrooms and office with smaller family and dining area... best choice depends on your priorities eg do you want to regularly entertain big crowds, what sort of WFH space do you need...can your WFH be achieved with a computer, desk and a bookshelf or do you also need space to meet clients and storage for sales equipment and supplies , what do you need for your prayer space, how much linen and bedroom storage do you want eg plan 1 has 2m of biw for beds 3 and 4 while plan 2 has 3m of biw for beds 2, 3 and 4, do you also need space for a computer nook, coffee machine, exercize equipment or hobbies with speciliased equipment like sewing machine and gardening tools??

having designed and built several similar shed homes my suggestions include variations to create more spacious kitchen, more private bathroom, separate laundry washroom and plenty of seating and strorage for crowds...upstairs has potential bedding for 16 including MPR and generous storage...locations for the bathrooms allow for the ultimate acreage luxury of a shower and loo with a view and assume that you will include patio/alfresco for outdoor living and suggest that reverse cycle AC is much more convenient and cost effective than an indoor fireplace