Same menu as a regular ADR.
You must give a CC to hold a Fantasmic Package ADR. You have 48 hours to cancel before they'd charge your CC.
Yes, you can book an ADR one of the participating restaurants and eat there but NOT do the Fantasmic package if you want to, but I guess if you want to eat there, you might as well do the package.
Yes, the package ADRs can book up so call early. Same with a regular ADR though. There are only so many of each.
IMHO, the package is only worth it if you go during peak season or a very busy time of year.
I've done Fantasmic with and without the package several times now and have decided that it's better doing it without the package. Now I can eat where I want to (or not at all) and then I enter either 1 hour or 45 minutes before the show and get great seats in the middle, about half way back. When I did the package, I still entered at 45 minutes before but sat to the far right.
The package seats are guaranteed seating (till 30 minutes before the show; then they can, and sometimes do open up to the general public), not preferred seating. They are off to the far right.