Hi Astri. I am in Canberra and have nineteen trees in our garden. How big is your block? Which way does it face for solar access? Do you have any power lines or easements to consider? What plans do you have for dealing with the autumn leaves? I'm not quite sure what you mean by a gatehouse and arbour on the fenceline but have you checked the regulations for structures on your boundary? Where do you want to plant the hedge and what is the width?

"Macyjean where do you recommend the vertical feature go...? Yes trying to make sure trees aren’t too large they cause damage to the property via root system and/or branches or fruit/nectar falling on the roof/gutters/paving." Somewhere on the left, but start with hardscaping, driveway, draw in underground services, think about what sort of footpath you want. I agree that it might be well worthwhile to get a landscaper to draw up a plan. "Thinking bay leaf could be an option...?" I remember going on a garden tour of a property with a park-like garden featuring large trees and the guide pointed out the bay tree and said people don't realise how big those get. There might be dwarf varieties these days though? "With the secret garden if I go teddy bear magnolia how do I layer plants to give varying height and colour while spacing them out for future growth? Is there a rule of thumb with number of levels/layers?" Just my opinion but looking at your photo and for ease of maintenance I think the magnolia with an underplanting of lomandras or something like that would be plenty. I can also picture three layers with flowering shrubs in between but I think they'd need regular pruning to look good. Lomandras don't need much attention, it's recommended to cut them right back every few years to rejuvenate them but it isn't crucial, whereas if you're going for a certain look with shrubs and don't stay on top of the pruning they can look quite scrappy and if you prune too hard they can take a while to recover. "What’s the rule of thumb for spacing of plants?" I think there might be some kind of general rule of thumb based on mature width? But I'd base it on the plants you choose. The label sometimes recommends the spacing, or if not the growers' websites have more information.

looks like one of the Philodendrons or similar plants that are usually grown in pots as indoor plants but anything growing in brickwork needs to be removed to avoid damage to the wall

I'd normally say go for a row of ornamental pears but I think it might look funny given your row of connifers as you don't want to look boxed in. I'd think about disguising neighbours with a single largish specimen tree in that side with lots of underplanting. You can't realistically block out all unattractive parts of outside your yard and what you really want to do is create interest in the foreground so it draws the eye in. Or else do the row of pears but create a bed in front of connifers and plant variety there (bearing in mind how connifers change soil acidity).