Any general dining tips for Walt Disney World?
Yes! I'm so glad you asked. Magic Kingdom has the worst food of any part. Get out of there to eat, if you can.
For lunch, take the Monorail to a hotel where the food is fresher, the restaurant less crowded and the service is better. Chef Mickey's at he Contemporary and 1900 Park Fare at the Grand Floridian are highly recommended. At Chef Mickey's, try the waffle. It's killer, as my 12-year old says.
Or, take a mid-day break and drive into Orlando. You'll find many restaurants, from fast food through family dining to upscale, all offering higher quality food at lower prices than inside the parks.
The ambiance in some of the Disney restaurants including San Angel Cantina at Epcot, the Coral Reef Restaurant, and the Rose & Crown Pub is unbeatable, so schedule at least a few. Consider making lunch your main meal. Full service restaurants are less crowded, and prices are lower at lunch. Similar entrees are served, although sometimes the portions are smaller - which is not necessarily a drawback, since you probably don't have a place to store a doggie bag, anyway.
Do look into making reservations at the more popular table service restaurants, especially if you will be visiting at a busy time of year. Any character meal will be booked solid several weeks in advance so if you have your heart set on one of these, planning ahead is key.
Can you have a Disney dining plan if you're not stying at a Walt Disney World resort hotel or resort?
If you are celebrating with an advanced dining reservation at a table-service restaurant, you may get a free dessert (at select locations). You will need to add your celebration at the time of booking. Disney occasionally offers promotions like free Disney Dining Plan with hotel and ticket purchase.