I can tell you from my personal experience... I moved from a Thunderbolt, which had 16GB internal, and I added a 32GB card.
I kept about eight movies on the memory card, and much of my music collection, along with photos.
Honestly, other then showing someone the Thunderbolt, I can't recall EVER watching a full length movie on my cell phone! I have a tablet, so if my family goes on a trip, I bring the tablet to allow my kids to watch movies on.
I've loaded my DNA with every app that was on my Thunderbolt, which I had used in the previous six months. I also went through my Transformer Prime, and loaded all of the apps from THAT device, which weren't on my Thunderbolt, but which I would use, either regularly or on occassion.
I also loaded about five albums... I don't listen to music all that often, generally only at the gym, for the 20 minutes I'm on the treadmill... and more often then not, I'm listening to talk radio on Sirius.
Checked my remaining memory about four or five days ago, and was surprised to see I have just over 6GB remaining! If I want to load a movie or two, or add more music, I certainly have the room.,
My photos, other then the ones taken with my DNA, are in my DropBox account, and DropSync uploads all new photos to my DropBox automatically.
Bottom line... I haven't had any issues with space, but your situation may be different. You do have until Jan. 15, I believe, to return the DNA if space does prove to be an issue.