For the official details on Salary Sacrifice use trhis link toi the Australian Tax Office site and run through the page links on the right hand side of the page
Salary sacrifice arrangements for employees
As far as a deposit for a home we always recommend 26% . So 20% to avoid having to pay whats called Mortgage Lenders Insurance (insurance to protect the bank not you) and 6% to cover Stamp duty, Legals, Inspections etc. You can get a 90-100% loan but the providers are drying up as the credit squeeze continues worldwide
As you will be buying your first home in Australia you should see if the stamp duty concessions apply in the state you are moving to while on a 457 visa or not.
Hope this helps
Liam