I'm not sure I understand exactly what you're asking in terms of booking activities but this is what I will share.
Regarding the photos with characters, they have meet and greets all week. When you first board the ship, go to the activities desk and get a ticket for the princess meet. We had pictures with all the princesses and it only took about an hour. They do this at a couple different times so if you book an onboard activity that's happening at that time, they can give you a ticket for a later meet and greet. The other characters are throughout the ship all week and have designated times listed in your navigator so you can arrange to be there and you can work all this in around any activities you've booked. You should be able to get photos/autographs with all the characters without needing to book anything special or interfering with any activities booked on board.
As for CC, it's my favorite beach in the world so I don't book excursions when we're there. I just want to enjoy the beach and water. I loved having a cabana but it does kind of remove you from all the activity so if you're interested in taking part in the scheduled events (they have character meet and greets on the island as well), you may want to save your money and just hang out on the main family beach. Snorkeling is pretty cool and they do have the stingray station and beach bike rentals right there on the family beach but you shouldn't need to reserve any of these things in advance.
