I agree with the other comments. They are a really tough plant. They are also very prone to spider mite - an occasional squirt of the foliage all over would help. A monthly application of very, very weak liquid fertiliser when watering would help along with a regular wetting agent. Weekly watering should be sufficient where you water until the water comes out the bottom. If more regular is required, then you need to repot.

It’s a great idea, that way you can alternate whenever needed without too much fuss, your balcony looks quite spacious so you can have some beautiful pots out there with the added bonus of looking lush from the inside, love these wall circles too.

For low maintenance in such a variable climate while preserving light access I think I'd go for some kind of a translucent decorative screen, with maybe just a few potted plants to provide some greenery. If they're not planted in the ground you'll have to be even more careful to ensure they get enough water. Or, thinking further, I've seen Chinese star jasmine used in challenging commercial locations, including as a screen around a cafe's outdoor area, it looks amazing and appears to be very hardy and copes with a temperature range similar to yours. Two drawbacks though, some people dislike the smell and it needs pruning so not low maintenance. It's difficult finding something that ticks all the boxes.

@bigreader thanks also. I just came across Angus' site tonight. FYI the man at the nursery also suggested I do "succession planting" (assuming that's what you mean) i.e. put the lilly pillys at the back and put a row of ?cant remember the plant he suggested? in front that grows more quickly than the Lilly Pilly so will provide screening in quick time up to 2 metres whilst waiting for the Lilly Pilly to grow. I opted out of because really I want the screening to create/fill in the border around the property - the reality is that the trees won't really act as screening much at all for many years (the trees need to get quite tall!) as the house up the back is UP THE HILL so unless they come DOWN their backyard (which they rarely do) the screening is not really blocking any views into my backyard.