Oh man, such garden jealousy/fomo right now. I really wish I could afford a garden atm! My aunties garden in WA has been commandeered by my manchild uncle so even if I go there for a few months there's not much I can do. Absolutely love those poppies. So striking!
You would know that famous little nature strip at the corner of Walpole and Malmsbury - owner replants seasonal flowers without fail - it reminds me a bit of that.
Ask for forgiveness instead of permission? π€ I see people quietly adding plants around street trees all the time.
With the visibility thing, I think if you stick to stuff under 0.5m you'll be good. There are some councils that allow nature strip gardening and specify the heights. Maybe Port Phillip?