That looks like it. Some call it crazy paving. It usually gets laid over compacted paving sand/s. The joins between each flagstone are usually concrete with the edges concreted so it stays in place. I have seen some with sand between the joins which also looks good. New sandstone from Gosford Quarries looks superb but is expensive. (its a great product!). I'd look for some second hand stuff on Ebay/Gumtree/etc.

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.

Hi Katrina, Overall the sofa looks just too big, even though essentially it fits on paper. It would be better to go with a 2800 L shaped sofa with chaise and have the chaise side running by the wall so it's a bit more open as you walk in. And if you make the chaise 1600/1700 then you have more room to pull the sofa a bit closer to the TV and make space for your dining table behind. Or pop the chaise on the side closer to the kitchen then you may have room for an occasional chair on other side by the window. Does this make sense?

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 :)