when I was in Sydney I stayed at an amazing hostel called "Wake Up!" This is their website: http://www.wakeup.com.au/
I stayed in a 6 bed girls dorm and I think I paid about $30 a night, but that was in 2007 and I just checked - it has gone up to $38 now (£23.66). That is quite expensive for a hostel, I'd say Australian hostels usually average $20-25 a night, but then Wake Up! has a great atmosphere and I met some brilliant people there, the facilities are the best I have ever seen in any hostel. If you just stay there for your first week while you get used to Aus and hostel living, you'll have a great time. Then you can always stay in cheaper hostels afterwards. Also remember that the more people in the dorm, the cheaper it'll be. I.e. 10 people sharing at Wake Up! costs $32 per night.
The weather can vary across Australia from May-August but in general I'd say it's like a nice English late-spring/early summer's day... t-shirts acceptable but possibly need a light jacket or hoodie too, kind of weather! I found it to be hotter in the north and cooler in the south. I worked in the south-west in June/July time and I had to buy extra layers as it got really chilly. But when I went to Cairns in August it was humid and almost 30 degrees. I didn't stay in Australia during their summer time so didn't get to experience the REALLY hot temperatures! I only remember it raining heavily twice when I was there, which is insane compared to the amount it rains here! Although they have recently had terrible flooding, so I guess it changes year to year.
I got work in a pub through an agency in Perth called "the Job Shop" which is in the backpacker part of Perth called Northbridge. Check out their website:
They have loads of jobs in different areas and are so helpful. They have computers you can use too. My pub job was in a town 10 hours south of Perth - amazing and one of the best experiences I have ever had.
As you're a guy you might be interested in some more intense kind of jobs like farming/factory work/harvest work? Or is that just really sexist of me?! I think if you put the hours in with those sorts of jobs you could make more money than pub/bar work. Although I got paid $14 per hour in the pub and got free food and accom which was brilliant. All depends what you're willing to do and how strong you are physically..and mentally! I met lots of girls who tried fruit picking/harvest work for a few days then gave up as it was backbreaking and they only got paid per container filled not per hour.
Hope that was useful to you! Amy :-)