I'm a Cast Member at Walt Disney World and can add a lot of clarity to all the new features of My Magic +
Magic Bands: These wristbands function as your park ticket, Fastpass return ticket, room key, and Photopass card, additionally you can sync your Debit/Credit card to it and use it to charge. They are incredibly durable and waterproof. Because you are traveling with a special event, I am not sure if you will get these or just a plain plastic ticket. They might give you a plastic ticket for the parks and a MagicBand for the room, in which case you can sync the two online.
My Disney Experience: You need to download this app and create an account on it before you go. You will then need to add any MagicBands or cards to the account so you can manage the plans for your party. You can sync cards to Bands here too. You can use this app to make dining reservations, but most importantly to pre-plan Fastpass selections. Some attractions will be gone by the time you get in the park, as regular resort guests can plan up to 30 days in advance. Take advantage and plan in advance! You get 3 starter Fastpass selections a day, once you use all of them up you can go to an in park kiosk and select new attractions, one by one. All your photo will also go to this account.
MemoryMaker: Buying this photo package gives you unlimited downloads of all the photos Photopass photographers take of you. It's expensive, like $200, but my mom said it was well worth it to not have to be constantly pulling out her camera. Plus Photopass photos are really great quality.
If anyone has ANY questions about anything at Walt Disney World, PLEASE ask me! If I don't know the answer, I can find it out for you