Assuming you are staying at a Walt Disney World resort hotel, you will be able to make reservations for your entire trip on the first day of your booking window (90 days from your check-in date). In order to activate this capability, you'll need to log into the system with your resort confirmation number.
For example, if you look at
THIS reservation page for the Crystal Palace, you'll see a box that says "Update Your Profile" and a place there to link your dining reservations to your resort reservation. If you do this, you should be able to make all your reservations online.
Since your reservation window is still a few months out, I would check back here from time to time. The online reservations system is brand new and there may be small changes as the system is tweaked.
Good luck with your planning!