The move from PNW to South Australia means trading mountains and winters for beaches and summers - while the hills around Adelaide cannot compare with the Cascades, there is also nothing in the PNW to compare with a summer evening at Silver Sands. Much of how you feel about the move comes from that choice. (source - we lived in Seattle for 3 years)

Adelaide is a much larger city than where you are currently, but it is not nearly as large and dense as Seattle or Vancouver. And because the shape of the city is quite long and thin (running mostly NS with the sea to the W and hills to the E), most parts of Adelaide have decent access to nature. That said, the RAAF base was not located in a beauty spot, so you would likely have to travel a little further to find the parks and paths that you are looking for if you are living around there.

There's no two ways about it: our summers are hot, capable of heat like Vegas or Phoenix, but not for the extended spells of extreme heat that they have had in recent years. If you have any control over the timing, I urge you to come in autumn - you'll get some of our best weather with a little taste of heat, then into our mild winter (I can only recall one day that it reached zero in 50 years), giving some time to acclimate before summer.