yes, it will impact your ftb entitlement
you will have accrued maintenance income credits for the years in which he didn't pay
plus the normal maintenance amount for this year that doesn't impact your payment
the maximum you would normally get per child is 160 (ish) depending on income
it will drop no lower than 50ish dollars per child
that's per fortnight
just want to clarify this one - your "entitlement" won't drop below $50 per fortnight but if you've been paid a large amount of child support in a lump sum, it may reduce your annual entitlement, and the c'link/fao system will automatically reduce your payment to counter any perceived over payment at the start of the year. because each of the payments is an annual amount, the system reduces how much you get so you only get your entitlment for the year - and the reductions can be fairly big