Consider a micro-inverter system. Less fire risk (and may actually be less expensive) as they don't need DC wiring in conduit all way back to the switchboard. They are quicker to install, not much more expensive overall now and much better system monitoring. The best micros are Enphase, they'd be the only ones I'd consider.
The system size to get depends on your usage. With only a low 6.2c/kWh FIT in Victoria now, you just need to replace expensive 9-5 grid usage with solar, and/or transfer some night time usage (e.g. dishwasher, washing machine) to the daytime. So you need to work out your 9-5 daily usage and the amount you can transfer.
For most households 2-3kW systems will be fine, anything over that may be over-sized and a capital cost waste, unless you are going to offset things like aircon in summer. You won't escape the daily service charge no matter what you put in.
The best orientation is due north, but for summer usage like aircon, think about a west-facing orientation that supplies a reasonable amount of power until into the early evening. With variable pricing under smart meters, the peak is now 4-8pm, so that's when power will be most expensive.
I have a 5kW system that I use to power the house, swimming pool filter, swimming pool solar heating and a 1kW garden watering pressure pump. Daily output varies from 3kWh on foggy winter days to 30+kWh in December. On a good day at the monent (late April) it will produce 21kWh. My quarterly bill is now about $150-200, without solar it would be $800-$900.
Think also about energy reduction like LED lights, energy efficient appliances, double glazing etc. I downsized a pool solar heating pump from 750W to 300W with an actual increase in heating efficiency. Saves about 2-3kWh per day in summer.