Hi, Emma. The best place to start is by adding photos, from the top of this page, to an ideabook on your homepage. You can put tropical Australian gardens into the search bar at top of page. Save the pics you like. Also, you need to add photos of your property exterior to this comments section here. Can also put them in a separate ideabook, so Houzzers don't get confused. A plan showing north, with dimensions, will also help you get really good advice.

With the deck being quite narrow have you considered taking the timber to the edge of the deck and not using a coping stone. This will give you a sleeker more clean lined look. With regard 90 verses 140 decking. We use mainly 140mm now, but with the deck only being 2 metres wide this may look out of place. A lot will depend on your surroundings. If the deck hasn't been started yet I would also suggest that you run your decking the short length, this will draw your eye along the lines and give an illusion of the deck being wider than it is and looking up it not as long. With regard cupping it very much depends on the timber selected and you really need to screw down rather than nail. For almost all of our decking I specify and recommend Accoya for its stability. I am sure that it will be available in Australia.

I was going to suggest that the shower and hanging for togs and towels be placed in the red zone using the pool house plumbing. It looks great where you have it but it should have somewhere for the togs and towels as kids will use them several times a day in hot weather. If the Pool House was a POOL house and open to the pool would that mean you could just fence it and the pool together, but I guess by being multi function that changes the rules

Google “opaque pool fence” https://www.tintingdirect.com.au/frosted-film-balustrade.html