Hi Guys,
Kalbarri is where I first started windsurfing. I havn't been up in October for ages usually I go just after christmas (well when I had uni breaks I used to .... full time work now

)
Anyway, if the sea breezes are coming in best to get out about 1030am - 11am on the river near the boat hire. Generally the breeze swings a bit later in the avo making the conditions more marginal, however the last 2 years I've been told that the winds have been howling in for longer.
I would recommend against sailing through the mouth. If you happen to run into trouble you'll likely wash up at a place called "Frustration" ... you wouldn't come out too good.
Having said that I've seen people go through there no problems ... only issue is when you have a problem.