Sara,
I think that will be a pretty good week to visit! You're right, the majority of Spring Break travelers will be gone by then, and the weather should be fantastic. And you'll be able to take in the beautiful Flower & Garden Festival in Epcot!
The meal plan is hard to answer, since some people love it and some don't. My family falls into the 'love it' category, as it makes our trips much easier. You know your cost upfront which is great for budgeting, and when you get to Disney you don't have to worry about paying for individual meals since everything is pre-paid and loaded right onto your room key.
One important note about the Dining Plan is that is definitely requires planning - you will need to make your table service meal reservations in advance! I personally enjoy that planning and feel it is a good part of our vacation, but if you aren't typically a planner then this will be different for you.
You can find more information on the DIsney website regarding
Character Experiences, and I also like
www.allearsnet.com. Just search for character dining and you can read reviews and even see complete menus!
Have a wonderful vacation!