This sounds like a great project!
I think a coaster enthusiast is just what it says. It's someone who is enthusiastic about roller coasters. Whether its how the feel while riding, how the rides work (a lot of us are nerds like that), the adrenaline rush you get while riding, or just getting away from life for awhile. It could be anyone of those factors or all of them combined.
I know for me, its really getting away from life and stress. I can take one ride on my favorite coaster The Voyage and all of my stress from the last 6 months just melts away. That's all it takes is one ride. While riding I forget about everything else except for having fun!
It doesn't matter about counts for me, or the mechanics of a ride or where it is, it's just having fun with life-long friends and getting away from life for a day or a few hours. That's all that matters to me.
Please feel free to private message me on here, I would be glad to help you with your interview.