Just in case you are asked for an AOS, here are the details from Centrelink: Assurance of Support
Your assurer will have to provide taxable evidence over the last financial year and evidence of ongoing current income.
Here's the AOS Factsheet: Australian Immigration Fact Sheet 34. Assurance of Support
As amaslam said, for the spouse visa the AOS is discretionary, so you may not have to apply for it.