Maptools.
I think I'll either be a mechanic, or a navigator. I assume that there is a mechanic right?
I would like to be a large part of away teams. Maybe a science officer?
The rolls are:
Rogue trader: Leader. (A player almost certainly has to be this)
Arch-Militant: Weapon master.
Astropath Transcendent: Powerful Psyker is the living radio. (Needs to be one, if a player is not one we need a npc.)
Explorator: Tech Priest. (This would be your mechanic. Not strictly needed, but if we don't have one it closes some stuff.)
Missionary: Priest of the god emperor.
Navigator: Mutated... Navigator. (Needs to be one, if a player is not one we need a npc.)
Seneschal: Expert in... Being second in command?
Void-master: Ship master.
The thing is, everyone is good enough at fighting. Sure, the Arch-Militant or Explorator might be the guy with the heavy weapons in some situations, but most of the time anyone can pick up a gun and blast away with the best of them. Classes are really about what nitch rolls they fill, everyone fills the main roll of damage dealer.
A important thing to note here. We are all very important people already. A powerful Rogue trader can be stronger then a planetary governor, or even a governor of a star system. We have hundreds of people working under us already, and the PCs who are not the Rogue trader are considered his inner council. We don't partake in normal economics and use money, we use influence to gain what we want on a large scale. Command of 10s of thousands of troops are within our grasp. Whole worlds can burn at our command.
So, this is not a little group of adventures running around in a small star ship, so keep that in mind.