I had these exact same questions! In the end I couldn't get an appointment for a time that I could actually go in, so I called up and spoke to a really lovely helpful guy. I've done my lodgement online, and said on there that bubs is due 04/06. They sent me a text asking to send in forms (I'm assuming they mean proof of birth & proof of income?) but I haven't done this yet. It was my understanding that I'd take in all the necessary info after bubs is born.

Also, they seemed to get the start date of my parental leave wrong - I want it to start after my work maternity leave, so 24 weeks after birth, but they have it starting on the birth date.

Anywho, after all that - you should be able to start right now!