Happy Birthday, Happy First Trip, and Welcome to the Boards!!
Disney is for everybody, and folks around this place agree it's for all ages...so please don't feel you're taking away from any of the families with kids if you want to (insert fabulous Disney experience here)!! The Disney experience is to be shared by everybody!!
And, yes, WEAR THOSE PINS and let Disney know it advance that you're celebrating!
The entire of Disney takes on an extra layer of magic at night, and you're going to have an EXTRA layer of magic on top of that, being there with the Christmas Lights up! mrhub had some great suggestions for you...I think you and your friend may feel completely occupied just by wandering around the World in the evenings, checking out all the Lights everywhere.
Some folks enjoy going to the other resorts to see their decorations. You'd just need to get on the bus from All Stars, and head over to the TTC and then take the monorail to the Grand Floridian or the Polynesian, for example. I hear those resorts are AWESOME that time of year!!
Welcome, and enjoy your planning!! 