Hello Annika,
July wil be nice. You'll be there for blueberry season. You'll be able to do a lot in 6 weeks, but watch out for the mozzies. I wish we were moving over there for good, but no, only 3 weeks at Christmas time. And yes, it will be cold. I hope there will be heaps of snow.
I've never lived near Greenmount but I know the area. It's very nice. I'm originally from Geraldton and that's way too hot. I can cope with Perth's summer but I don't like the heat. We're in Mandurah at the moment and it's not too bad, but we still get some hot days in summer.
I'm not a huge fan of Sydney. It's just sooo big!!!!!! We were there for a holiday last month. I lived in northern NSW for 10 years and that was beautiful. There are some really nice spots all over NSW.
So what's your link with Finland? Annika is a popular name in Finland. That's my sister in laws name.