I presume you've had a read of our blog on this site?
We only spent 1 week on a campsite, the rest all wildcamping. There is no problem with paring on the ports during the winter; I don't suppose there would be any issues in autumn either, as Italian wildcamping is verymuch alive and well so I guess they'd still be there - maybe capacity mihht be an issue.
There are so many places worth visiting it's hard to pick any in particular out, but might single out Sellinute, Trapani and the salt flats, Segesta and the Baroque towns in the east of the island - and definately Villa del Casale and the fish market in Catania ...........
So much to see - you'll love it!