We have made the run from Rainy, across into Namakan, and down through Sandpoint to Crane Lake a number of times, albeit not in a C-Dory. It's a nice trip, but we have found those lakes to be more crowded than Rainy.
As far as beaches and Rainy go, we seldom land at them as even the finest-grained of them can harbor rocks. And houseboat tie-ups can be among the worst as the houseboats have steel pontoons and are unaffected. I would never overnight beached for fear of being ground to smithereens were a blow to come up. But there are some good docking sites to tie up to such as Kawawia Island, Anderson Bay, and Kettle Falls itself which has quite a system. But as has been stated, numerous anchorages abound and that is what we prefer, just swinging in the breeze.
Al