I agree, clean it up and keep it simple and let your plants be the star. The photo doesn't look very dirty sometimes the patina of age is better. Trim up the rosemary or lavender on the left and put something bright into the terracotta pot - you could buy a more colourful pot. Small pots can also be put onto the wider steps but not too many as it can be overcrowded. Be careful of overflowing plants as they can make it shady and encourage moss. Keep the plant colour palette limited- you can't go too far wrong with white or lavender tones. An aged wooden seat or similar would look good at the base of the stairs.

annb1997 - Yes, that is part of the reason I'm doing this project. The entire area will be lowered, re-graded and some drains installed (the garden edge is kind of temporarily in place for now, got a great deal on the plants so they had to go in). It's a bigger job than anticipated as it also means the air conditioners (x3) need to be de-commossioned and re-installed at the new levels. John, I like the idea with regard to the tank, but we get allot of bitey critters and I don't really want to give them anymore areas to hide out in.

making a mould and pouring the concrete would be your best bet in getting the look you are after, you can buy the smaller ones but I think the large one you may have to do yourself or have made, lots of info on making them on Pinterest.

There are some messy native trees like gums and quite tall Grevilleas but I’m happy to cut these back. I’m not sure if a formal garden will suit a new timber vertical batten style fence which will be quite high for privacy, 1700mm.. I’d love more plant suggestions, love bird of paradise, grasses but I know they can look messy.