Somewhere on these pages, a whole Grand Endeavor is written out to do this, and it is EXPENSIVE. -10 Profit Factor and 30 years of time are just two sacrifices you will need to make. Please don't forget the silly scale of some ships in 40k; their "regular" fighters have at least half a dozen crew EACH, and the Light is a monstrously huge battleship. Also, she is seriously damaged, and many parts will simply need to be pulled and replaced.
In addition, you would need thousands of Tech-Priests (50,000 of several varieties), six times that many Servitors, and whatever it will take to bring all of that to the hulk. Moving those resources is not a secretive action. Once the ship is fixed SOME, you might be able to move it to a safer place, but that will hurt the ship, too. Finding battleship components is no cakewalk, either. The ship uses large mounts of numerous other substances, some of which are hard to find.
This all assumes that Roth and the Tribes have been dealt with. Roth is insane, and only wants to fly his ruined vessel, which he feels can never be repaired, into oblivion. Getting through the cobwebs in his head to convince him you might actually be able to return the Light to greatness would be VERY hard, and the idea of his ship just being destroyed, to keep it out of bad hands, or chopped up for its various parts is nightmarish to him. He could sick the Tribes on you, and there are many thousands of them on the ship, all over the place. His own implants might make him rather hard to kill, too.
If you COULD get them all to help, you might have some good aide, with the Iron Kin able to serve as some low-end Tech-Priests, the others workers or guards, and maybe provide a few of the others with escape. Then, it's still all of the above work.
Lastly, there is still the Dread Pearl. If they are playing that campaign, they don't really have time to stay and play with the Light, and the rewards of the over-campaign are supposed to be amazing. They could leave some folks there, but their safety would be hard to ensure, and after you leave, any of your competitors might find the wreck, and send it off, or claim it, themselves. Sometimes, it seems wiser to get the quick loot, and send the ship off, so no one else gets their pick at things. They could also show up while you are doing that, as the books says you might toss any of the opposing RT's in at any point, to spice things up. Better you send the ship off than let them have a chance at it, after you leave.
If you search the forums for Recovering the Light of Terra, you might find the very cool write-up I am referring to.