Hi Polly, we did the Western Isles last year from Oban to Castlebay then up through the Isle's to Stornoway and back via Ullapool, we used a Hopscotch 8 from CalMac ferries.
There is loads of free/wild camping and a good few campsites (though expensive) I have some maps and a book of the area if your interested.
Have a look on the Calmac site for routes of Islands you can get too and the cost, if you require anymore help just ask.
P.S. Polly there is an excellent writeup in Feb issue of the C&CC mag on the Isle of Skye well worth a look and it is a great 1st venture into the scottish isles