A group of us done this a few years back, we hired Canadian canoes from somewhere in FW and arranged for the guy we hired them from to pick them up.
Really cant remember many of the details, it was a good laugh and we were far from experienced.
We took tents intending on using them every night but on the first night we stayed in the youth hostel which was near lagoon, but i think this is now closed.
The second night we stayed at a hostel in Fort Augustus and the third night we camped somewhere by the loch side.
We were taking it pretty easy and I think that if you went at it with more conviction than we did it would be doable with two night.
It was good fun and the only annoying thing was having to lift the canoes out of the water and along the towpaths at the locks.
It was good fun