Hi Victoria,
What you're hearing about Fantasmic is true. It is only held on select evenings so the nights it is performed it is super popular. People start lining up at least 90 min in advance.
The Fantasmic Dinner Pkg can help significantly cut down wait time & includes choosing lunch or dinner at 1 of 3 restaurants:
* Hollywood Brown Derby (lunch or dinner)
* Mama Melrose's Ristorante Italiano (lunch or dinner)
* Hollywood & Vine (dinner only)
It also includes seating in a reserved section for Fantasmic. The section is reserved but the seats w/i the section are not & are available on a 1st come basis. If Fantasmic is held on more than once on a given evening, the dining pkg is only available for the 1st show. Call 407-WDW-DINE for reservations which can be made beginning 180 days prior to your trip.
You are welcome to bring food & beverages into the theater. There are also limited concessions available in the theater.
Once they open the theater, you are mostly on your own to find seats. They will make announcements to move all the way to the end of the rows & Cast Members (CM) will do their best to help scout out seats. If you are traveling w/ a guest in a wheelchair, you can see a CM as you enter the theater & they will assist you in finding a seat in designated handicapped sections. Only 1 member of the party is allowed to sit w/ them & the rest of the party is directed to companion seating if available.
I recommend that those planning to attend Fantasmic go w/ the frame of mind that you're in it for the long haul & plan accordingly. Bring something to keep you entertained while waiting outside & inside the theater - especially if you have small kids. Its worth the wait & good things come to those who wait.