Hi Deb,
I did the c2c mid winter during a week of big storms. Watching the storms smashing the coast (and us) and getting completely nailed by horizontal hail is something I will never forget - It was a lot of fun!!!
If you're not very trackfit (used to carrying +15kg on multi day walks) I would strongly advise taking a good set of walking poles & gaiters. There are long (8km+) sections of soft sand beach walking which, with carrying 18kg, will make your legs feel like they've never felt before.
A short pair of light weight ankle length gaiters will stop your boots filling with sand - non-beach and dune sections are also pretty sandy. In my case the sand caused friction which caused big blisters - OK until we ran out of strapping, then
VERY NOT OK.
You're not supposed to camp anywhere except designated spots. Having said that we were forced behind a sand dune for one night because Willyabrup brook, dry in summer, was a 3m deep raging torrent when we tried to cross it.
All the camping spots are good. Contos campground is a big family camping spot but was still really nice, and also good for fishing and a swim.
We mixed our accommodation - for instance 2 nights camping and 1x night accom. This enhanced the trip really nicely for us, although I appreciate that many would want to stay in the bush full time.
Probably the best money we spent was on the souhern leg - we called 2 hrs before Hamelin Bay and got picked up, fed home-made dahl and wine, and then dropped back off the next morning by a groovy couple (ex new york hippies) who run Wren Cottages. Stayed in their large onsite "caravan" for about $100ea per night. Link:
http://wrenwoodchalets.com/index.html.
Best of luck.