Hi Daniele!
I think it's a fantastic plan to have some non-park days during your Walt Disney World vacation! There is so much to see and do outside of the parks, you'll be glad you took the time off. We often said years ago that we never spent enough time exploring our Walt Disney World Resort hotel, so we started adding resort days to our schedules. It's also a great way to relax in-between hitting the parks.
You are more than welcome to enjoy a character meal on a day you are not visiting a theme park. Any restaurant located at a Resort hotel or Disney Springs does not require a park ticket, so planning a character meal on your off day is a great idea.
Advance dining reservations are highly recommended for Table-Service meals, especially character meals. You can make reservations up to 180 days in advance.
My favorite character meal is
Chef Mickey's at Disney's Contemporary Resort for brunch. I love visiting with Mickey, Minnie, Donald, Goofy and Pluto and brunch offers the best of both worlds between breakfast and lunch
Have a magical day!
Leslie