I understood that if XW is primary, she pays everything and then gets CSA.
If Australia is like the USA, the person who receives child support also decides how to spend it. It sounds like your STBXW prioritizes being a good mom and can be trusted to fulfill that role well so you are fortunate there. I only mention that to prepare you--some non-primary custodians get grumpy their money isn't used the way they expect.
