I spend a year travelling and working there, and spent a reasonable amount of time in Tasmania, Melbourne and Brisbane.
Weather- Tasmania’s not all that different from Europe, weatherwise. It doesn’t get so much of the incredibly hot stuff, and it does actually get rain on a semi-regular basis. I presume you’d be planning to go to the mainland though? Well, it depends on area a lot, but yes, it can get far too hot (and cold- and switch between the two really fast! The year I was there, Christmas day was actually colder where I was, in Melbourne, than where my parents were, in Northern England- but only two days earlier, it was meltingly hot). But air-con is so widely available, unless you’re working outside, you can work around it a lot.
I loved Brisbane- it’s decent size city, modern, friendly, lots of stuff going on- good nightlife, but not just a mad party place. It’s possible to find reasonably priced places to live there- I can only directly compare rent to the UK, but I had a place cheaper for a short-term contract there than I do here, for a similar size, and it was in a much nicer area. It does get too hot, and when it rains, it rains.
Minimum wage is high compared to Europe, I think wages generally are higher- and house prices are lower than Western Europe certainly (my cousin, a nurse, and her husband, a plumber, recently bought each of their two daughters a house, pretty much outright. My mind boggled.) Food prices I’d say are higher, clothing is suprisingly expensive, but it’s hot, so you don’t need to wear so much of it 
You might encounter redback spiders, and see a snake hightailing it off under a bush, especially if you go somewhere rural. Just don’t poke them. The dangers are massively overrated, same goes for sharks. I did meet one person who had been bitten by a shark (a wobbegong, yes, really, he poked it). Redbacks do show up in cities (said cousin did have an infestation of the buggers once) but most people just count them as a nuisance rather than a serious threat.
It’s a pretty safe country, so long as you don’t do dumb stuff like head off into the outback to wrestle taipans and forget your water bottle. The violent crime rate is low compared to just about everywhere, I didn’t feel threatened at all, that I remember. Slightly skeeved out by bogans with no sense of personal boundaries when it came to girls, but that was about it.
There are religious enclaves around, but religion is not a big deal to most Aussies (my cousins excepted, annoyingly). Apart from my family, I don’t think the topic even came up in the whole year I was there.
Tourists are common, and largely English/Irish/German, with a few from everywhere in Europe, and to a lesser extent from the US and Canada. Most tourists are concentrated on the East coast, Melbourne and Adelaide. And Uluru. Obviously.
Hope some of this is helpful!