The stronger the beer the better it will last. 7% + should be able to last 12 months in a keg easily.  A weaker beer will do at least 6. Flush with CO2 before filling of course... 
 
You want 12-20 degrees ideally - upper end of that for ales and lower end for lagers. 
 
Looking at this:
Yinnar climate, averages and extreme weather record | Meat & Livestock Australia
April and October look like the best times of the year to brew. 
 
If you are going to that much trouble you may as well buy a grinder,  mash tun and a fermenter and do all-grain brews.
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