Regarding the issue of whether an idea for the story should be "roughed out" before we begin:
Personally, I see the idea of planning the story elements almost as re-inacting the story. If we already know what we're doing, I wonder how interesting the story will be to role-play.
Also, the odds of getting everyone to agree fully on a rough story idea, are relatively slim. We will spend more time planning the RPG than actually taking part in it.
I'd prefer to take a chance, and see where they story goes by improvization. As long as people adhere to the guidelines, it should work out nicely. Worst-case scenario, we'll run out of ideas. We have enough string writers on these forums though, that shouldn't be a problem.
The top priorities as I see it, are:
1) As Malte mentioned, that the main LBT characters don't get ousted by our custom characters. Any custom characters should remain relatively minor.
2) The story is plausible for an LBT movie, and no outrageous elements or strong language is thrown in.
Perhaps we should just start one, and see where it goes. I'll leave that in your capable hands, Malte, unless you'd prefer otherwise.