If a story diverges it'll move to its own thread. Otherwise I'd post to the thread that your story continues (thats kind of the big thing, continuing the story. My GM NPC just wrote himself out of the rest of the arrival RPs, but someone could easily pick up and continue any portion of it). So someone could post watching the merchant prince arrive and witnessed the exchange with the guard from a shadowed building entrance before going to spread the word that a new head honcho has arrived etc.
As for separate persona threads that's up to you all. Generally speaking there isn't really a need, but it may help people jump in later.
