I was asking mostly to see how much boat I might need for conditions. The conditions you describe won't be a problem in pretty much anything I might charter.
You are correct. Before we bought the diesel cabin cruiser we ran around the San Juans in our first boat, which we still have: a 17' Arima sport fisher. (photo). We'd launch at Skyline in Anacortes and run across Rosario Strait to our property in the islands and then spend a couple of days on the boat. We did this year round. We'd watch the weather, of course, and we wouldn't go out when it was real rough. But most of the time we had no problems at all, even in February.
I don't know how many people you're going to have with you, but popular boats in the islands are Nordic Tugs (26,34, 37 feet), GB32, 36 and 42, all sorts of Tollycrafts in the 26 through 40-something feet, Bayliners in every size imaginable, particularly the ones in the 30 to 40 foot range, and the sport fishing boats like C-Dorys, SeaSports, Grady-Whites, Trophys, Arimas and so on .
You can run around in the island in just about any weatherand be fine. The only bodies of water that can get pretty nasty are the ones around the outside of the island cluster: Rosario Strait, Haro Strait, Boundary Pass, the east end of the Juan de Fuca Strait and the bottom end of the Strait of Georgia. You have to cross at least one of them to get into the islands themselves. But most of the time they're in a pretty good mood so no problems.