Hi Heidi,
What a great graduation gift you have planned for your daughter!
You would have to call the team at Disney Dining for the exact price for the upgrade to the Deluxe Disney Dining Plan. I would then go to Allearsnet.com and price out the meals you have planned. With this simple calculations, you will be able to determine if you need to upgrade or not.
While you may save money with the upgrade, you also want to look at the amount of food which is offered at the meals. If you traditionally do not eat appetizers and desserts, you may want to pay for the cheapest meals out of pocket.
As for too many sit downs, it is your family's preference. My family generally eats breakfast in the room with foods from home and then grabs lunch in the park. We usually do a sit down dinner because we like to take a forced break and we can chat about how to spend the evening and the next day. Sometimes we do a special breakfast but then we did a lighter dinner to make sure we did not use extra meals.
However, this is a special occasion and as long as you are not breaking your budget, add the Deluxe Dining for the extra magic!
Wishing you a magical vacation!
Beth