Stevie129 is right, I'd try and apply for PR from the UK prior to coming out. I'm currently on a 457 visa myself and finding it difficult to get another hospital to sponsor me on the same visa. You will get private midwifery jobs easily however if you want to be able to utilise your skills I'd recommend looking for work within the public sector.
Accommodation: My husband and I are in WA and when we first arrived we stayed in a long term rental for 3 weeks in order to enable us to search for a permanent rental and get a feel of the different suburbs. We were lucky to secure a place after only 1 week of looking. Before we moved out we read on here that the rental market is very competitive and be prepared to do viewings with lots of other potential applicants. Don't know if it was luck but we did the viewing alone and our application was accepted straightaway. We just made sure we had the money for the bond and at least 2 weeks rent upfront. And the estate agents contacted my manager for reference (this was only to confirm that they have employed me on a full-time contract).
Shipping: we shipped almost everything we owned I.e bike, tv, clothes, books etc....of course our bikes didn't arrive until at least 2-3 months after we had already settled in by that time you've forgotten half the things you shipped and when they arrive you're like why oh why didn't I just throw these things away or sell them! Lol moral of the story...you'd probably find it cheaper to buy things when you arrive or ship the absolute essentials! A lot of people buy secondhand stuff on gumtree to start with until you get established into your own place.
Transport: I would recommend budgeting enough to buy a car as soon as you arrive. It will make your like 100 times easier especially with getting around with the kids.
Other information: Start sorting out your nursing registration with AHPRA, once you have eligibility to register with AHPRA then start searching for jobs. Sign up with job alerts with public hospitals in SA and check out jobs on seek.au.
Wish you the best of luck.