Hi Matthew,
I am a huge fan of the Disney Dining Plan's flexibility and financial benefits. My family uses the plan every chance we get.
You are correct that the number of Dining Plan credits on your Key to the World cards (room keys) will be determined by the number of nights you'll be staying at a Disney resort. Therefore you'll have five days worth of credits per person. However, you are not required to use a certain number of credits per day. You should have no trouble using all of your credits during the three full days you'll be visiting the parks. You can use them for breakfast, lunch, and dinner. You can also book a special meal at a
signature dining establishment. These luxurious table service restaurants take two table service credits per meal. Be sure to call (407) WDW-DINE in advance if you wish to dine at one of these fabulous restaurants. In fact, that's good advice for any of the table service restaurants you'd like to try.
Another good strategy for using your credits is to pick up a quick service meal to go at your home resort on your day of departure. Unused snack credits can also be redeemed on single serve treats in your resort's gift shop or food court. I always stock up on Mickey-shaped rice krispie treats to bring home on my last day.
Let us know if you need any more advice as you plan your upcoming Disney adventure. We'd be delighted to help!
Jill