@DolphinSquared, after the Applications come in and we choose the Gym Leaders for 2015, there will be a separate forum for Leaders to facilitate the fleshing-out of their "Gym", whether it be mono-type or based on a specific theme. There will be some time in between this and PAX, and will include edits and peer-review. I wouldn't get too hung up on not having a fully fleshed out back story from the get go.
@Kaka has chimed in below with a few swell ideas! Or you could check out what we had for 2014, that's a good start
I am still particularly proud of my backstory, but obviously I'm not sure how many challengers could have told you why I had a pocket full of Ghosts?!