We have similar and they spread. We didn't plant them but I think birds have picked up seeds from else where and dropped at our place. We back onto a National Park so are getting rid of them, but you have to dig and get the roots out as well as they regrow quite easily... Ours get a bright red/orange flower head on them which look ok but not great in a native area..... Pull them out, roots and all and bin them.

Perhaps check with your local council to see if they have a plant list. Many councils here in NSW do this to assist homeowners with choosing native Australian plants and some introduced plants that grow well and are in keeping with the area. Of course it depends on the look of your house and whether your landscaping plan will compliment that, or whether you want a manicured look, or a natural look, cottage garden look (e.g flowers and hedges) or a beachy look (e.g. if you have a pool) and so on. Fruit trees sometimes need a different aspect to other trees, so separating food trees from general foliage is something to consider. Oleanders are off the list in many parts of NSW too. We recently put a fence in similar to yours but it has been painted black as our house is modern. We've been advised on lomandra, banksia and grevilias and lili pillys for a native garden as we already have lemon scented gums and ironbarks on the property. If you consider the building style of your home, and the trees common to the area you're in, sometimes that can give some inspiration

Julie Herbert - thank you sooo much!!! I have seen these trees and wanted to know the names of them :) ...and now i know..I was googling fireworks trees hahaha. Thanks again!! I'm sooo happy now~

@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.