Wow, she's really pretty. Is she missing a toe on her back left foot? Also, I like the little heart shaped spot on her side. Did you rescue her, or did you buy her from a pet store (which, I guess, is still considered being rescued)?
Keep in mind that crested geckos are arboreal (they like to climb). I'm not sure what the measurements of a 5 gallon tank is in inches (length x width x height), but usually, the taller, the better. However, that can depend on the size of the gecko, in grams, as well.
Cresties are very...
I agree with Silas. That would be great if you made it into a vert enclosure, which shouldn't be to hard to do. Crested Geckos would LOVE the extra height. Another question: How big is the crestie you're considering (weight-wise/grams)? That can have a lot to do with the size of the cage as...