Great! 

So for a quick update on my thought processes for this, I have planned out some of the more plot-intensive details, and have the world totally fleshed out in my mind. 
I'm thinking that we will start somewhere on the eastern coast of the U.S. 

I'm open to suggestions on whether or not the story should start during, before, or after our characters meeting each other though. 

Unless of course you were aiming to be a character that should not start with the party, like the president who would have duties to uphold in the capitol, or any person which has a clearly defined position of power that would prevent them from being on the coast. In which case you would start wherever you are needed.