With income you can earn up to around $170/fortnight, then lose 40c in every dollar while on single parent payment (I can't tell you exact figures as I'm on a different payment. SPP has more allowance that I do).

Child support is based on the same rate. If you can calculate around 8% of your partners wages(for one child), that would be an estimated amount of child support you'd receive... as long as he pays.
This is where it can all get really confusing though. Even if he doesn't pay, centrelink will base your payments on what he should be paying, then will make it up at the EOFY. So an estimate now might be a good idea, because you are prepared to not rely on that money.

It is tight. I have friends with under 3 kids that are paying around $270 per week. Rent is getting higher where they are now though, they're really starting to struggle & down size, or going back to relationships that weren't particularly healthy for them.

I don't have any magical solutions for you. If I did, I'd be using them. A lot of the time when you have to count for fuel & child care, working is pointless... I live in government housing, but still really pay the same as everyone else where I am (if not more), because I don't get rent assistance.

It can work though it's just a challenge