This seems interesting. How would you coordinate the "choose what the character does" part with people taking turns writing posts?

If it helps, here are a few past RPs that incorporated similar concepts to what you want to do:

Mystery of the Key: full disclousure, I ran this one. A group of writers took turns writing for all the characters, shaping the plot and world as they did so. The RP can be found here: https://www.roleplayerguild.com/topics/187004-mystery-of-the-key-a-collaborative-writing-story/ic

Wal Quest: a guy ran a choose your own adventure style story here for a while. It's pretty strange, but the mechanics might help you. It is located here: https://www.roleplayerguild.com/topics/184216-wal-quest-interactive-post-apocalyptic-quest/ic

Use or ignore those if you want. I'm interested to see how this idea of yours develops!