The parlour palm is the most reliable palm for indoors .. Plants add exponentially to the indoors effect and personality, as has been said many times over, however as with anything, ideally should be placed/chosen tastefully and not in a hodge-podge or messy looking fashion. Unhealthy looking plants are particularly unattractive ..

On the top level you could grow both edible ginger and turmeric. Growing these plants will allow you to enjoy their flavours in your food from your own garden. They would also give you a background level for the whole garden. Some of the cherry tomatoes would also give you a ground cover and plenty of fruit on another tier. Checkout the lovely grevillea ground covers on the net. The bottom tier would be soft with some of the grevilleas available.

Not sure how it would go in Brisbane but what about trying a conifer? They grow fast and very tall. You can shape them or leave them natural. They are plain and certainly not tropical. Maybe speak to a local nursery and find out if they would grow in the sub-tropical climate of Brisbane first, as they are usually in colder climates (Sydney and south). Leightons Green Conifer – Leyland Cypress http://www.evergreengrowers.com.au/shop/hedging-screening/leightons-green-conifer-leyland-cypress/ Your quite limited if there's not enough sun and you dont use bamboo or tropical plants. Many other screening plants or hedges wont get tall enough for that space and climate. I hope you find something.

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.