Hi Emma,
I am in Sydney were honey is collected all year round and I only ever use 1 brood box on 10 frame hives. In the Blue Mountains the bees will be fine, however if using 8-frame hives then definitely 2 brood boxes is the way to go. You might like to also consider a different type of bee too, it is not really considered that much here in Australia as the italian bee is dominant, I run mostly caucasion bees and found them to give me a good honey crop right after winter as they do not eat through their stores like the italians do and have a longer tongue for getting deeper into the flowers. On average I get a larger honey crop from my caucasion bees throughout the year, and I keep this fact to myself amongst my local beekeepers and club members. They can have their little pretty yellow bees, I’ll stick to my grey average looking bees and sticky propolis. 
There are a few blue mountains beekeepers on the forum who can let you know how their bees are performing, there is a good thread at this location:
1 Like