The Mazda will get in, just take it easy. If it happens to start raining hard when you're camping either get the car across the creek quickly or wait a day or so.
It can be anything from cold to hot in the daytime in September and nights will be cool to cold. You seldom gets crowds at Moonarie and never many kids. The cold winter nights would have seen to the mice.
You'll find sweet drinking water in the newish tank in the descent gully above Top Camp but, yeah, bring a couple of big containers of general purpose water.
The crows and the callitris are part of the experience! Don't leave rubbish bags hanging from the trees - the crows tear them apart. Moonarie is a great place.