Oh yeah, those of you using that character generator I linked should note that you start with 500 XP, not the usual 400. If you took a Package like Johnfalcon did add +100 XP to whatever is left on the generator's Starting XP and it should work out. It's probably best if you spend them on advances beforehand. Think in terms of what your character would be good with. In this campaign I plan to use every skill at some point. While Basic Skills can still be used without training you probably don't want the half-value penalty that comes with untrained use.
I also encourage you guys to figure out how you were placed on this ship. To give more background, your adventure begins aboard a Free Trader ship called "The Wandering Pilgrim". The Pilgrim travels with a convoy flotilla for safety and their route primarily winds between Port Wander and Scintilla. Its current captain (spoiler: he dies) makes his living for the most part by providing travel options for all classes of Imperial citizen. The poorest are typically Hivers enlisted to colonize a newly secured world in the Koronus Expanse and are on their way to Port Wander where they'll catch smaller ships taking them to their destination. Because their fare is paid by others (and in the Imperium, life is cheap) they usually get stuck in the massive Cargo Holds normally used to transport goods. Sometimes WITH the goods. Nobles may be traveling anywhere in the Calixis Sector or be there for the ship itself, either to enjoy the Pilgrim's impressive luxury facilities or to do business in a pleasant neutral-ground environment.
Characters who are pilots or otherwise skilled with a Void Ship are easily explained as existing crew members. If your character is Void Born he or she may even have been born on it. Even Guardsmen/Arbitrators can easily be counted as among the many local forces used to keep order aboard the ship. These characters are also going to know things about the ship that characters from other backgrounds won't.
If you've got something crazy, like a Moritat assassin from a Feudal (i.e. Medieval) world, you'll have a bit more work to do but it can be a rewarding experience.
I might have to come up with some contrived circumstances to get you all together once the action starts. For the first adventure expect a lot of combat, some piloting of smaller space craft, tech-use, and a bit of cipher breaking. I've got quite a few ideas of how your characters can accomplish the primary goal (with various difficulties associated) but if you run out of options you'll be in deep trouble. Fate points can only get you so far.