Mark's guide choices are good ones. His comment about "it will be wet" and the other about cabin heat are spot on. For cabin heat I'd recommend forced air as it does a better job of fighting humidity. Air circulation in the cabin is important - the forepeak, the aft end of the boat, and where things are stowed that block air circulation are good candidate for mold to get started. Bringing wet things inside the cabin to dry, like foul weather gear, doesn't help with cabin humidity which needs to be below 50% RH to avoid mildew.
An enclosed dodger is a real plus; however, in any event, a good dodger is a must.
Grenville Channel: I'd avoid it going or coming. There's really not much to see and sailing it is a pain due to the canyons. We enjoyed Principe Channel much more and, unlike Grenville Channel, there are numerous good anchorages.
As a rule, the further inside you go, the stronger the canyon winds will be due to higher mountains with canyons. Constant wind changes in direction and speed. On the other hand, a couple of the low lying islands on the outside where we anchored had bloody horse flies: Gillen Harbor and Dundas Island to name a couple.
Don't stock up on tons of food items, but instead, spread your money among the small villages and stores along the way. They'll appreciate it.