Yep I used to work for one of those smaller companies that used to rip people off, they ripped their employees off too so we all quit

. Go for a larger company, it will cost you more, but when the time comes to claim anything on warranty they will still be around to fix it.
How big are your bills? You should aim to try and negate your bills instead of trying to go into the positive, when you have massive systems and make money out of it I'm not seeing the government letting you not pay tax on that for long. Solar is too new in Australia and will be changed massively in the next few years or so.
Have you got enough roof space? They should send someone out to scope you're roof and take dimensions, just don't let them split your panels on different facing aspects of your roof (say 4 panels facing north and 4 facing east) as you lose generation this way with most inverters. If you have to do it that way, ask them if the inverter has multiple power point tracking in it, if not, you will lose power.
Ahh if you're switchboard is not up to scratch they will need to update it to today's standard and it's not cheap. 90% of the jobs I did, I had to upgrade the switchboard while I was at it.
Yeah, any other questions? Just ask, im sure I left things out.