Best to steer clear from the original crew and their story. It's not like the Battlestar Galactica reboot, which took a good idea that was poorly executed and made it much, much better - even decades later, Firefly still has a solid fanbase who feel very strongly about the show and the characters. But I think there's plenty of the 'Verse left to explore: before or during the Unification War, during the same timeframe as the original series, after the movie. Loads of locations and strong characters. Loads of stories waiting to be told.