If my flight from Australia is several hours late will my reservation still be good?

Yes it would be.

Absolutely, you can also give a courtesy call just to inform them , or by email because I had problems with contacting by phone but yeah

Yes

I believe when you make your reservation it gives you an opportunity to put your flight info in the system. That should protect you if things happen.

Yes - they are very good about that

I think yes, mine was 1 hour late but I still got my car

Ours was good.. it was just two hours late..