The background is "wrested from a space hulk". A spacehulk is more the just ONE derilict ship floating in and out of the warp. It is a smashed together mass of different hulls and other stuff blunged into one odd shaped thing.

So… a huge logistical problem is ahead… WREST IT FREE FROM THE HULK. This only makes sense if it is already on the outside of the Hulk. But you will still need a lot of explosves…and before that a lot of exploration, so there should be an exploration challenge to find the spots where the explosive needs to be place. The longer this exploration takes, the more obstacles your can throw at them.

Finding all those leaks and damages that need to be dealt with should be an Exploration challenge as well…with a lot of focus on Trade skills (Voidsman; Technomant; Shipwright, etc). 

Decision: Dealing with the dead
Their are a lot of coprses onboard the hulk. Void mummified corpses of the forma crew. Giving each of them the bare minimum of sacrament (some final sentences by a priest before they are jetsoned into the void) would take a lot of time (penalty to Achievement points) but not doing so will be harmful to the moral of the crew (voidsmen do not feel if they treat the remains of their own kind like debris). What is the decision of the Lord-Captain? And what will the ships clerical class think of it?

Decision: Sanctification
The clergy urgently supposes a complete re-blessing of the ship. Given them what they (all the pomp and circumstances possible) will make verybody feel well in regard to the re-comission of the ship but will cost a small fortune (again, Achievement points). Simply deniying will make the ship prone to bad fortune and will damage the moral of the crew.  But what is the middle way? (Scholastic Lore (Imperial Creed) to know what is pomp and what is important). 

Decision: The Rites of Mars
The Technomants want to repair EVERYTHING but the ktichen think. The Recyclators deem the majority of the ship to be scrap and go about their business by the rule of swiftness ("if I already dismantled it, no technomant can do anythinig any longer"). If the Reclaimators are not but onto a leash their will be actual damage to the ship. But if they are kept onto to short a leash unreasonable afford will go into repairs as the Technomants will try to restore things better given to the scrap heap. It is important to make some key decisions here and restore order to the operation

I just ran a heavily modified version of Shades on Twilight from the DH adventure trilogy Purge the Unclean. The Acolytes were sent to recover an artifact from the wreckage of an Inquisitorial ship compacted within a space hulk. There were mumified bodies everywhere, members of the crew who's souls were devoured when the ship's Geller Field failed. Half-way through the ship, the group encountered what appeared to be a survivor- a man in robes pacing amongst the bodies mumbling "…total lack of discipline… no excuse for abandoning your posts… I obeyed my duty… now we have unauthorized personel on the ship… unacceptable… back to your posts all of you do your duty…". When the party's psyker used psyniscience to try to determine if he was possessed, he discovered that the figure wasn't really there, it was just a psychic projection. The figure got increasingly agitated as the Acolytes poked around, eventually screaming "Back to your posts back to your posts back to your posts!" before fading out- and the dead bodies begin to stir…

In small numbers, the warp zombies were much too slow to seriously menace the PCs, but the sheer number (the ship had a crew of 1500) they would have to fight through on the way out (yes, Horde rules!) would jepordize their mission. The robed figure kept appearing near the group and mumbling to itself. Eventually the party figured out that it was the ship's astropath: during emergencies, some ships enclose the astropath in a special armoured compartment with its own self-contained life support system, so they can continue to broadcast through anything short of the destruction of the ship. This being an Inquisitorial vessel, the compartment was additionally warded against warp energy. The players realized that the ship's astropath was still alive, enclosed in his armoured compartment and rendered hopelessly insane by the time the ship spent trapped in the warp (40 years- or just short of Eternity from his perspective), making it necessary to locate and breach the compartment and kill the astropath to nullify warp zombies he is subconsciously animating. This led to an interesting 'duel' as the astropath's avatar hurled a series of psychic attacks at the PCs while they tried different weapons to breach the armoured chamber.

It always seems like the local authorities are warning citizens away from space hulks- with good reason! On the other hand derelict ships are so valuable that everyone flocks to them whenever they appear; if only to steal everything that's not nailed down.

Imagine how upset the Imperial Navy would be if mariners had to risk their lives to chase the explorers into the wreckage for "rescue" , as a personal favor to that powerful warrant-of-trade-toting family. If they get a significant amount of sailors killed, that sounds like the opportunity to flesh out a nemesis! If the Navy can't or won't do it, then it might be time to call in the marines. The Adeptus Astartes, would more likely just destroy the party on sight (just to be sure), but they would also be no less pleased and probably would immediately eject the party from the space hulk and maybe turn them over to the Inquisition for good measure.

At that point it could become a cat an mouse game as the explorers, woefully unprepared to directly challenge a squad of space marines, try to outwit and evade the Astartes long enough to stake a claim, remove the ship from the mass and secure it as salvage.

None of this takes into account that the Astartes could always use an extra ship and what navy person doesn't want  "salvaged an entire Prefect-class void ship for Him on Terra" written on their resume'? That kind of temptation might make an otherwise incorruptible officer do something low and criminal just to further their career.