i have a thing for the Sunshine Coast. Combination of the greenery, warmth, laid back, yet an hours drive to Brisbane (large city for amenities). Large hospital opening next yr - good for health care for new kids.
Downside, yeah they get some storms during summer and you'll get some humidity too.

Gold Coast I think has more high rises giving it a bit more city feel, attracts some young idiots as the place to be in QLD to party. Hence I'm not a fan but I'll go there to visit.

Perth is otherwise my favourite city. Very laid back, less hustle and bustle than the east coast. Kings park is a massive, beautiful green park in the city to hang out. Swan river sees boats, jet skis out ie people having fun. Compare that with the Brisbane river. Perth is remote but I guess if you don't mind flying then the other cities aren't far! In terms of getaways driving distance I think they head south. Don't underestimate the Margaret river region. It's not only wineries but WA has an amazing pristine coast line and although there are still some coasts to visit in Oz....I think WA has the best. You'd be hard pressed to tire of it. Busselton and Dunsborough are nice little settlements also. I'd say Albany is driveable, Esperance better suited to flying. In time if you want to do some road tripping, northern WA has a lot to offer. there is coral bay, Ningaloo reef, the Kimberley ranges, national parks.... Both Perth and WA I feel are vastly underestimated as both a tourist destination and place to live. They have had some issues with fires due to hot weather just south of Perth but there's been fires in the other states also. Perth sort of closes down early in the evenings....which won't matter if you're not into night life.

Ive only seen Syd and MEL from the 'city' perspective which others have commented on already and have only visited friends or family in suburbia a few times. They seem OK....but they're just not my favourites. Climate wise MEL can be very cold in winter, and on the flip side I've seen it be ridiculously hot!! Sydney's climate seems a bit more stable and pleasant.

I can't comment on cost of living but petrol is cheaper than NZ and going out for a meal seems cheaper also. Housing? Well....there are some sales for sunny coast house and land packages from $300,000 being advertised on billboards.

Good luck with it