And don't worry, that plastic ticket will work for everything you need it to: park entrance, FP+, even linking to PhotoPass photos. Just make sure you've linked it to your MDE profile.
If you have an existing Band from a previous trip, you can use it on this trip. As long as both the new ticket and the Band are connected to the same MDE profile, they can "talk" to each other.
If you don't have a Band and you want one, you can purchase one in the park, but it's just a convenience factor. For all basic functions available to an off-site Guest there's nothing a Band can do that a plastic ticket can't.
-Rob