I've got a couple of ideas for meeting all the characters you want to in your dining plans. If meeting Pluto is more important than eating at a new place, do Garden Grill for lunch on your Epcot day, then you can do 1900 Park Fare on your departure day. OR instead of doing Be Our Guest for lunch on MK Day, do a late breakfast (I think the last reservation time is 10:30) and book the Wonderland Tea Party for the kids, which I think is at 2 pm. I don't prefer this 2nd option as much without cutting something out because it is a lot to pack into one day, especially after MVMCP. There is also the fact that the adults and Tank would not be allowed to attend because it is only for kids. Keep in mind you will also be able to meet the characters in the parks if you have to cut anything out. Alice meets at both Epcot and MK, Ariel at MK and during the Christmas party and Pluto meets pretty much everywhere.
We do one of the parties every year and we inevitably need to rest too. Depending on how crowded it is, we like to stake out a table outside at Casey's for dinner before the fireworks and then we have a nice view, if it's too crowded you can always take your meal to the hub grass. There will also be quick service restaurants open throughout the night as well as snack locations with nearby seating if you just need a quick break, and it won't take up too much of your time. The people watching during the parties is a lot of fun, so many festive outfits!