Your idea for them finding Trask by being psychically pulled to him works well. I have already made it quite clear (as is also clear in the original campaign but never elaborated upon.) that there is some kind of psychic pull that makes them want to posess the dread pearl. Im not entirely decided who made this happen but I imagine it is the Inquisitor who set all this into motion. That or the Witches of Footfall. (Who are controlled by one of the saner parts of the broken hivemind that is The Many.) He was the one who lured Trask to seek the pearl in the first place.
Trask has undergone a limited transcendence. His mind is disconnected from his body but he is still trapped on the sphere. He has been able to reach out through the webway to communicate with others though but only for a short time.
I like the idea with his mind wandering. He was a bit crazy even before.
I was thinking of giving them a ship but as they have already came into posession of their long lost flagship of the dynasty it feels a bit underwhelming no matter how powerful. Not to mention it diminishes their earlier accomplishment.. (Their second ship being Sarvus Trasks old ship that was lost in the Processional along, now renamed The Vintage since newly rebuilt ships keeping names of lost ships is in my campaign considered an ill omen)
The way I have portrayed the sphere is it is insanely advanced. It has nanobots that literally eat other ships or boarders, fractal robots, disassembling walls. Things like the concepts for the X-Com FPS would fit well.
Im thinking there might be separate individual consciousnesses within the sphere with different agendas that download themselves into robot bodies when needed.
Their decisions will likely be important for the future of the imperium but I just cannot figure out what the choices should be. I prefer if their choices limit themselves to the future of the koronus expanse and calixis rather than the whole imperium. (Though I was thinking of a follow up campaign in searching for the two lost space marine legions). They should have large long term consequences but not make the players themselves super powerful. (Of course they will also get rewards but those are separate)
The inquisitor wants to create the hydra, essentially a warp god built up of a human hive mind. This is dangerous and possibly a plot by Tzeentch. If done the right way it might work though.
The Many wants to repair itself but even if this works a revived Yu'Vath empire would not be very nice. They originally attempted to transcend so they could overpower the chaos gods and the oncoming Tyranids they had witnessed in a vision. They brought billions into the processional and forcibly separated their minds from their bodies and made them become part of their hivemind. Then they sent the empty bodies to battle with warp constructs controlling them. To humans this looked genocide and horribl using undead but to the Yu'Vath they were doing them a favor. The souls were after all still alive and now part of a larger, better whole.
Hmm perhaps the players could make someone take control of the Yu'Vath to use them as weapons against the oncoming Tyranids, awakening Necrons and forces of Chaos?
Djanko Scourge is dead, his son Varnmed Scourge wanted to avenge his father and thus allied with The Many but then the players threw him into a hellpit and he ended up swalloved by a demon of The Many so he now acts as The Many's spokesperson with only parts of his old self left.
The Dread Pearl itself is loathe to involve itself in the affairs of mortals. There are some parts of it that are curious however. Like children playing with ants. Perhaps the larger consciousnesses of the Dread Pearl are long since gone and all that is left are the stupid (by it's standards, superhuman by ours) defence systems and maintenance systems?
The defence forces might be able to speak and communicate and to humans appear as an alien race of robots or aliens but to the larger consciousnesses of the Dread Pearl this is just like an immune system. It is an idea at least.
I am not sure what Trasks ultimate goal is. He probably wants to reunite with his body.
Admiral Bastille just wants the Pearl for himself, probably as a weapon. Which wont work at all, the sphere just wont comply.
The Eldar wants to use it to further their own goals, possibly to quicken the birth of the unborn Eldar god; Ynnead. They have been in this game for a long time. They made the players astropath have her soul merge with that of an eldar soul in order to use the soulbond to create a psyker powerful enough to activate a path to the Pearl. (Without her knowledge and before the campaign began. This is only a small faction as most Eldar would consider such a thing a hideous abomination and probably want the Farseer in charge punished severely.)
Feckward wants to backstab the Eldar he has allied with and keep the Pearl for himself.
Blitz? He doesn't think that much, it's a marvellous gem to add to his collection. It's also a really cool thing for picking up guys and girls so that's a pro as well.
Lady Sun Lee is greedy above all else but loves adventure too.
Charlabelle wants to revive her dynasty but she is willing to cooperate with others. In the end she might sacrifice herself for the good of the imperium.
AMGEV Prometheus wants the technology within the Pearl, they might even come to worship it as a manifestation of the machine god.
The tech that could be gleaned could be an enormous treasure. Somehow I want them to make a choice of what path to take. Like in the Deus Ex games but my imagination is lacking here.
Ork ships crashing into the sphere im definitely gonna use, I want it chaotic but also scary. Seeing orks literally devoured by black clouds down a hallway for example.
Im definitely gonna have some gun emplacement blow up an enemy ship as well, possibly saving the explorers vessel in the process.
There are countless npcs with the players as well. The rogue trader Eleanor Trask's mother; Isador Trask (A very demanding, passive aggressive woman), Sarvus Trasks closest friend and lover; Wrath Umbold. (The RT does not know of this but her mother does. Wrath and Isador Trask do not like each other AT ALL) , Asira Stormcaller (Who was Sarvus former Astropath who were driven insane in the processional and left behind on Dross) got killed in a crash and was ressurected by their insane Adeptus Mechanicus Genetor and is seeking a new purpose in life as her psychic abilies has been robbed of her. (She claims her old self is dead.) Theres their crazy, overemotional and enthusiastic Adeptus Mechanicus Genetor; Jeanette Ironfang who keeps wanting to "Improve" everyone on the ship
Then theres the players I haven't mentioned.
The crazy AM Techpriest Ezekiel. (Who is now paranoid about the Eldar, keeps putting up lights everywhere after meeting an Umbra, thinks Orks are gonna pop out of the woodwork and keeps screaming over the voxlink for no reason.)
Their controlling, Stalin inspired seneschal: Jarrion Rautamäki who has created his own security forces called the nightwatch and is essentially controlling most of their ship by now.
The insane Astropath Lucretcia who acts a bit like Max from Sam & Max but in her more lucid moments is a brilliant strategist.
Then theres the one sane woman aboard the ship. The Rogue Trader Eleanor Trask who has been driven into alcoholism by her collegues.