Scale is what you make it!

Start small and build up to whatever is comfortable. Why not try an alternate timeline or even an "After the Dragon" plot. Even if nobody knows how the series will end yet you could extrapolate and make up a finish that you like and play from there.

Don't limit your choices, and most of all check what you players like. This can be the source of some of the best plot ideas and will make the game more enjoyable for them as they fulfil personal goals built into your world.