Hi, Rebecca! You can dine anywhere on Walt Disney World property, whether you are a resort guest or not. As long as there are still table available, you are welcome to come and eat, shop, or just browse around the resort. I love doing that!
If you haven't made a reservation yet, you can go to
Disney Dining Reservations and see what's available. Some restaurants can get busy, so check as soon as you know which day you'll want to visit.
As for the theme park, I'd probably do either the Magic Kingdom or EPCOT. Are you taking a shuttle from your resort to Walt Disney World? If you are, you can just hop on the monorail at the Grand Floridian and be at the Magic Kingdom or EPCOT in a few minutes. If you have your own car, it's a quick drive into either of those parks as well. You may want to see what time you'll be having breakfast and make a decision based on that. I prefer the Magic Kingdom if I can get there early, so if breakfast is later, I'd go with EPCOT.
I hope this helps! Have a great vacation!