1. No, or yes to a very minor degree. I think aliens might detract from the story line, especially if we play as rebels, or if we're dealing with a human threat.
2. Some form of war sounds the most interesting. Though, if we're pirates, it would be more challenging to play in a peaceful period, as the government would have more resources to focus on pirates.
3. A stolen battle cruiser would make for an interesting dynamic. But we would need to roleplay how we... "acquired".... said vessel.