Hi Jamie!
I'm so glad to hear you're starting your little Disney fan out at a young age! We've visited Walt Disney World with our children from the very beginning (7 weeks old was our youngest), and there's so much to look forward to!
Walt Disney designed his parks with the family in mind, so you'll find that 99% of the attractions your son will be able to experience. Here's a nifty list of the experiences that have height requirements. All told, there are just a handful of things out of all that can be experienced at Walt Disney World.
Magic Kingdom:
Big Thunder Mountain Railroad
Splash Mountain
Space Mountain
Stitch's Great Escape
Tomorrowland Indy Speedway (will need to ride with an adult so they can operate gas pedal and help steer)
The Barnstormer
Seven Dwarfs Mine Train (once it is opened)
Epcot:
Soarin'
Mission: Space
Test Track
Disney's Hollywood Studios:
Tower of Terror
Rock 'n' Roller Coaster
Star Tours
Disney's Animal Kingdom:
Expedition Everest
Dinosaur
Primeval Whirl
Kali River Rapids
As for the formula, Walt Disney World carries Carnation brand formulas, so you'll either need to pack some, or order some on amazon or gardengrocer.com and have it delivered to your resort. I'd just suggest packing the formula, wipes, and diapers in a bag, and on your return trip home, you can utilize the space occupied by the baby necessities with souvenirs!
If you choose to order from amazon or the like, make sure you have the delivery address formatted as follows:
ATTN: First & Last Name
c/o Disney Resort name
address line 1
city, state zip
Arriving: D/M/YR
Resort Confirmation Number
Have a magical vacation!
Amanda