If you decide to do it just have a backup plan in place and be ready to use it - living here, my experience is that the ferries are not as reliable and punctual as some are making them out to be. Summer with the day boat operating is better but there were numerous days when the ferry was late and the day boat has been out of service for a period of time each summer from hitting logs in the water and such. As for flights, fog is usually more of an issue in the fall, if you are here in the summer I wouldn't worry about it as much.