Ferries and tours on Santorini

Abby, well, I also went to Santorini in June (2017), then Naxos by ferry, and I also stayed at Villa Fotini, also thanks to Janet. Great spot. About the ferry, I did book my ticket online while in Athens, and was then told to go to the ferry office in Fira to actually pick up my ticket, which I did a day or two before. Maria at Villa Fotini arranged for a taxi to the ferry port at the time I needed. (It is different than the cruise ship port, and is not very convenient.)
For a day tour, I took an excellent one, also suggested and booked by Maria. It was all day, and included the Akrotiri archeological dig, the small village of Megalochori (which I enjoyed so much I returned the next day by public bus), a Santo Winery visit and tasting, a beach stop (for the beach and/or lunch, which you can pay for), and a few other scenic stops. The morning pick-up was right near Villa Fotini. As I remember, the price was €45 per person, very reasonable. Then, for an additional €5, instead of coming back to the inn at about 5 pm, the bus (without the guide) would take you to Oia for the sunset hours, leaving Oia again at precisely 9 pm, for the trip back, dropping you by Villa Fotini. So, it was a great value for a loooong day, including an excellent tour.

Hi Abby, we are doing the same (also with kids: 2 teens and a tween). We bought our ferry tickets in advance. I went to the ferry website. I chose SeaJets from Santorini to Naxos because I preferred their schedule (I think the first Hellenic Seaways departed at noon and SeaJets was closer to 10a). I don't know if the schedule changes as the season picks up. I was told on these forums that you don't need to by tickets in advance and can get them a day or two ahead at the port, but this was not something i wanted to do while doing other fun things. I prefer to have ALL my tickets for a trip on me when I leave for the trip and then just pull out (or pick up) the ones I need when the time comes).
We also booked a Catamaran trip around the island. My husband spearheaded this so I don't have great details, but its a 5 hour trip with dinner and sunset. You stop at a beach and some mud baths. Time is 15:00-20:00, but there its a morning excursion as well. We found the company on trip advisor after studying several and reading a lot of reviews. The tickets were ~100 per person. This is our splurge for the whole Greece trip (even typing that made me little nauseous ;p )
Hope that helps (oh, we will be in Santorini first week of July)

Edited to add: and because I am a commitment phobe, the ferry tickets allow for cancelation up until [can't remember which] 7 or 14 days before departure for a full refund. I had booked with Hellenic, then canceled them and changed to SeaJets, and the cancelation was smooth as butter

We enjoyed the same island tour as Larry per his recommendation last September. The only difference was, we decided to forego the Oia evening stop and went there the next am by bus to avoid the crowds. We were very pleased with the same Caldera view at dinner that evening in Firostefani. Highly recommend the tour. We did not do the Catamaran Tour, but another couple we met was taking it the following day. The same company provides this tour as well.

We did the same or very similar tour as described by a couple of other posters. We also skipped the sunset viewing in Oia, since we were too exhausted for anything beyond dinner and bed. There are many spots from which to get great sunset views besides Oia, and you can visit there by public bus for very little money.
I’m guessing that any hotel manager/concierge can set you up with a tour.

Larry - do you remember the name of your tour or the company that provided it?