The roaring twenties sounds like fun. A new and interesting setting that today's media tells me was an interesting time for crime. The 90s were great, but I lived through that decade, so been there done that. Music was awesome though. 

And I have to agree with the first simplified plot. It gives a base for a more elaborate plot to be developed. If you start out with such an open world, I feel things can turn to mush quite easily and quickly. A simplified plot keeps the players focused and players are less likely to stray the story off.