I believe shared care is where you visit your usual doctor for your regular check-ups, and then visit your OB or the hospital for the major check-ups and scans etc.

I chose to have all my care provided by the OB, but that was due to my history of m/c and I felt that I would feel better about things if I was seeing the specialist on a regular basis. It's entirely a personal decision and you should do whatever you feel comfortable with doing.

If you went through a public hospital for the birth, you shouldn't have to pay anything (provided you don't chose to be admitted as a private patient and wish to specify your doctor etc which is a different scenario I believe). Perhaps you could get in touch with the Health Insurance Commission or Medicare to double check this. In terms of private hospitals, what you would pay depends on your level of cover you have, and what (if any) excess you have attached to your policy.

HTH!!