Hi Clarie,
Looks like I am in a similar situation like you, so I've stumbled upon this topic here.
I'm also considering to move to Sydney because of a job offer. I don't have kids tho, so my case is less complicated. I have been offered a job with a 457 visa too. Husband and I are thinking about this one very hard, mostly because of 457 related issues listed below by VERYSTORMY and northshorepom.
While we are thinking, we are also researching.
We would love to live in some family-friendly, pet-friendly, calm part of the city. Our best option would be something in Freshwater - because of a job location. I've googled a little bit and I've found some websites with suburb list and suburb profiles in Sydney. Maybe this will help you to get familiar with prices, schools, etc.
Good luck!
