This is an interesting topic. We just moved to Sydney and I have four kids (and am far from rich) lol.
I had one (wierd) woman stop me at Town Hall station and interrigate me about whether or not I was rich and how I can afford to have four kids and some wierd stuff like that.

I don't know the answer to all your questions above as we just moved here three months ago, but I'm learning about where cheap shops are that have regularly reduced fresh foods - meet, produce, dairy - that is definitely helpful.. plus budgeting carefully.
My kids are at a public school. A lot of their clothes have been hand me downs or gifts which helps too. As for room sharing, they actually prefer to share a room - they are still young though. I cook most of our food rather than eating out.
As for cars, can't really answer that - right now I'm borrowing a Toyota Echo - tiny little car LOL I hope to buy a second hand mini van of some sort soon though.