Yes! Why not! I'm more than "a tad" older than you and can see all the inappropriate plantings here and wish I'd not been so adamant, stubborn and even enthisiastic and passionate back then. I'd like to imagine you 20 years from now enjoying the beautiful fragrance of your plantings and not having to remember, looking at your aged, sore and tired hands, how hard was the task of taming and imprisoning the devil in lilac! There comes a time when even one's passion becomes a chore...Nobody is exempt. My hands are crippled with arthritis. I cannot get a grip on my brushes, thus the hard work has deprived me of a pleasure and a passion....that is the way it is for many so I hope you are immune. Unfortunately ageing is what the body once strong and virile does and it has no mean influence on that part of a creative person's life. I will imagine you 20 yrs from now, sitting peacefully and enjoying the tenacity of your younger days...not wishing you had done anything differently!

GOOD professional advice is worth every cent of what you pay. If it was my property, I would ignore the upper retaining wall and plant at the bottom, selecting a plant that will screen from the bottom to above the height of the fence. Its also much cheaper this way. There are numerous lily pillies available that you could consider. I would choose something like Syzygium 'Pinnacle' because of its eventual height, its adaptability to different soils and sites, and because it is relatively narrow. Its also fast growing. It is a conical grower. Plant them 1.75 metres apart or thereabouts, working the spacing depending on the length overall and then just nurture them. If you retain the the conical shape, then you wont need to hedge them - just leave free standing or trim the width a bit. Then bring in some taller trees that will grow higher or at least as tall as the Pinnacle - I would use deciduous to allow winter sunlight in and have large garden beds under the trees linking the whole area together with lawn or lily-dale toppings or similar. Lawn would be better for the children, but will need irrigation [in summer only if necessary]. And if growing lawn under trees, you need to be selective with the lawn type considering shade, tree roots etc. I know that people mock the use of lily pillies, but these are people who don't know what they are talking about. The knockers have grown lily pillies that are inappropriate to the position and because of their stuff-up, the whole range of wonderful plants gets canned. The right plant to the site is called sustainability. Councils/government are opening up a lot of areas that were once considered wet-land. So a lot of these new subdivisions do have drainage problems, and buildings with their footings increase the movement of water, increasing the drainage issues. Small gums, like the Eucalyptus leucoxylon ssp megalocarpa is a wonderful tree for soaking up excessive moisture. This is also worth adding to the tree mix, especially to shade western windows. Good luck with your project.

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.

Thank you so much for your advice, in particular to bigreader and Julie Herbert. Here's a photo but note Im awaiting all that timber to be removed and daughter yet to sweep up the potting mix. I tried a blue one on each side as well but it didn't look quite right. I actually think 2 on each side might be enough. Note, in the big pot on left is a ground cover that will sprawl and out and done pot all going well. Do you think/Any suggestions for anything else I could do in this area? I'm still getting used to colour of mat. Now for the back door. Ive put some pots there that I had painted a light grey. Im wondering if they dont provide enough contrast with deck. Your thoughts? I was going to put a buxus in the one on the right (purely because they're are numerous in garden I can poach).