...How's this work? I am a writer, and I realize the chances are like one in a million, but you have to live your dreams! thoughts......hows the process work?
Your best bet is to query a list of agents first, see what their responses are.
Although, writing what is essentially 'fan fiction' isn't really what a lot of people are searching for. Your characters are already someone else's. Gotham is a city that is already imagined.
I'm a writer myself. My advice to you would be to change the script a little, and make it your very own project, a work constructed entirely of your imagination only.
Then again, fan fiction does have a chance to make it, albeit a slight one, so in the end it is up to you.
I just don't see the point in you doing all the hard work to heighten someone else's story. Make it your own, from the characters to premise, make it original.
Good luck.