There's an estimator on the family assistance website that you can enter your details into and see how much you may be entitled to.
yup, this is probably the best option

the impact your working has on your payment depends on a lot of factors - age of youngest kidlet, how much your other half earns, how much you earn

you can earn about 4500 per annum before your ftbb is impacted BUT that same 4500 may have an impact on your ftba depending on your partners income