Hi, generally the ferry schedules offseason are not that good. Usually, just one ship a day getting to the most destinations.
New schedules every year come out around March. Santorini is an all year round destination, however, I find it better during June or September when it doesn't get too crowded. In November sometimes it might be a bit cold, it depends on how windy it gets. For instance, this November and earlier December were pretty hot around 18-20 Celsius. Of course, that is not the case every year. For ATV rentals check santorinibikerental . When in the Cyclades it is also a good idea to try Greek Island Hopping, check this by Hostelbay.com if you are on a budget