Too add more to the initial post, this is what Im thinking,

The story will take place parallel to the Straw Hats journey. We will never cross paths with them but this is the prime One Piece Universe. We will roleplay a crew(s) on their own journey through the world of One Piece and the Grand Line. We will visit mostly different islands than the straw hats and maybe well see the aftermath at other islands.

We would start in one of the blues, Im leaning West or South but I havent decided yet, and work towards our own side of Reverse Mountain. 
I will try to organize it in a way that this will constitute a solid saga complete with character arcs for everyone to develop and play through. If people have ideas for an island and story we can absolutely work to incorporate them. This is One Piece, there are millions of islands, and the stories are just as numerous. 

I want to keep clear though that this will be casual. Have fun with it and do stress out. This will be chance for everyone to explore ideas and grow in their roleplaying and writing abilities. I wont try to restrict people much as I want it to be fun, and keep people coming back to it, so go wild with ideas.