Yes there is a $200 deposit required for vacation packages. The remainder must be paid 45 days before your check in date. Cancellation penalties or change penalties kick in after final payment is due, 45 days from check-in.
The alternative is to make a room ONLY reservation right now, which requires a deposit = to one night cost of your room, and the remainder is due at check in. The cancellation policy is more generous for room only packages and is either 5 or 7 days from check-in. I've been told both recently but would go with 7 to be safe.
If you book room only, you CAN add your tickets at a later date. You can add dining plan at another date if you wish. Most people add their tickets within 7 days of check-in, and that allows you to have your tickets attached to your room key which simplifies things for most of us.
Also, even if you book room only right now, you can have them reserve the Magical Express on your reservations, and when you know your flight information you just call and give it to them. Another perk of staying onsite that you may as well use if you can.