Proportional consistency - keeping the 1:2 rule in place everywhere will jar less than having the same architrave but varying the skirting. If you’re already considering 90 and 140 skirting, why not go for 40 and 70 architraves? The effect will be more harmonious and it shouldn’t impact the price too much ... plus, it’s your house - if you like the 1:2 rule then use it :-) (PS: if it does impact the price too much, just pick one size of each and save more cash)

do you mean glass louvres?? pool safety is too important to compromise but ask your appropriate state agencies if properly fitted security screens would meet regulations

I would talk to your pool builder about the pool detail. They are the experts.

No, and it would be better. Left as is, the people that sit at the island, will be sitting in the walkway, and the space in the dining and lounge, being only 4340 wide, would be compromised. It is not just the width of the island bench, you need to also take into account the room taken up by people sitting at the island. Could be, Maybe another 500mm into your lounge and dining area. Shown on your plan as theatre?