[Dunadin777]

I think you're missing the perfect option for your game: let the players stumble into something epic. You don't have to start out with a grand scheme in place. Instead, let the players start out with random, freeform adventures. As the first few sessions go along, watch their interactions with key NPCs. Don't just blithely follow their impressions--in fact, I'd recommend running counter to their knee-jerk reactions. If they immediately have an unfounded distaste for a fellow crewman, make him become an integral part of the crew, the one who is dependable when all else fails. And that NPC the characters either ignore or pleasantly dismiss? Have him develop into something twisted over the course of their adventures. When the NPCs develop into epic characters in response to player action, it will help them to feel engaged by the story and it will help you get some great ideas over time for where to go with the developing plot.

Just my two cents. Of course, my current campaign is a little bit the opposite of this: I have my players freely running around with only a vague hint of what's really going on, while the villain is on a track to take over the world in about ten years' time.