Like Marja said. It is not a good case to date with a girl with a balloon fetish because you have a balloon fetish. The chance is quite big you date with her because you lay too much pressure on the fetish. It is the best when your first dates does not contain any balloon activities because you can learn eachother.
If I would find a looner girl which I could date with I first want to know her more about her character than dive directly into balloons and so on. The inner person is much more important than the outside (if you know what I mean).
After a while maybe I would involve balloons, but that depends how the girl is and if we are still dating.