All campsites are 2wd. But can have a few potholes, especially Banksia green. Beach access last time I went was very limited, thanks to the Nazi's at NPWS. Would not be surprised if its been reduced again.
The toilets aren't pit toilets, their those eco-toilets, smell like a pit toilet but
No showers at any of the sites I've been to.
I wouldn't worry about a crowd at the time of year you've mentioned.
I think some campsites have fire pits, but banksia green is one of the "put it where you want" campsites. There's a board as you come in telling you if there's a fire ban or not, given the time of year, there's a good chance there will be (so make sure you don't see this sign on your way in )
There's a little tap on the dunny blocks for washing hands only, and its also small and low pressure, so not really suitable to filling any containers with. If you need just washing water I'd go up the road and get it from the lake. Water there is pretty clean, just a bit yellow from all the tea trees lining the bank.