Will post my personal answers for when I did my HSC. I'm short on time so please excuse the poor expression.
1. ~ 5-6 hours per night.
2. Nope. I used others' state ranking notes and added to them. I mainly spent the time saved on doing exam questions.
3. Yes. AS MANY AS YOU CAN DO!
4. Yes...
LOL!
I had some of the best teachers, and the best teachers all advise that tutoring is an efficient and powerful way of preparing for your assessments. I owe a lot of my success to my tutors.
But yeah, it's a debate that's been done before =]