The thing with casual work is you can just work at one hospital on bank and if they are short of staff will book you but can cancel you some places have a condition that they can move you to some other ward instead if you are not needed where booked.. Or you can work for an agency and go to different hospitals but can also get cancelled sometimes after you have arrived at hospital.

Some hospitals dont have agency work in birth suite just post natal.

Doing casual most likely you will only do birth suite if hospital allows it but mainly postnatal.

Depends on hospital and state how easy it is to get shifts.

Good luck