So, this is going to be mostly opinion, and also a bit complicated, and/or silly of me to ask, but here we go. Your character obviously isn't going to be the only Rogue Trader in the galaxy, even the Expanse. Say you decide, however, that you don't want the solution to every other RT being violence; maybe you possess a sliver of realization that the galaxy is a big place, and there is a place for other like-minded individuals, provided the two of you get along. How are two Rogue Traders, big egos, bigger ambitions, and all supposed to come to amicable agreements? So many altercations in RT between various Lord-Captains basically have to end in conflict; it's fun, dynamic, and a good source of XP. You might get battle experience, might get rid of an enemy competitor, might even get a hold of a new ship, and all the spoils, wealth AND info, aboard it. So what is our good incentive to be diplomatic about it? I very much like Lure of the Expanse, and it and Edge of the Abyss each document a nice assortment of very cool Rogue Traders, your peers, betters, and enemies. My problem with Lure, however, is that, even something so massive of an undertaking, you can finish yourselves; no nice acting toward the other Rogue Traders is required. Some of them are blatant tools, yes, but even the ones who might be agreeable to cooperation are nicely written to not act that way, leaving you with the need to be social, and there might be little reason to make long-term partnerships with any of them.
So, in your games, do you ever make reputable arrangements with your RT peers, and not the kind at gunpoint? Taking them hostage and using them to produce you an heir to you Dynasty, and thus maybe seize theirs, is great, but not exactly polite, nor is backstabbing them when it becomes appropriate. How do you form a partnership with someone like that? What did you do to accomplish it? Is the grimdark just not a place for such enterprises?
On to the second. Rogue Traders can often get anything they really want to, from new ships to new planets, and practically any weapon they could want, even a relic, if they are connected enough, but how do they get more "exotic" stuff? Here, exotic reads Eldar, but you might have others. Ork stuff is junk, and many other races willingly sell their wares, if you are interested in such things, but Eldar are aloof and arrogant enough that I don't see them willingly "selling" their gear, even as their needs grow, their surplus gear sits, and their population falls. So did every Rogue Trader with an Eldar power sword kill an Eldar (a Banshee, a Corsair, probably not an Autarch) to get it? Could there be terms where again, violence isn't the only solution? Charabelle Armellan in Lure has a Harlequin's Kiss; am I to believe she actually killed a high-ranking Harlequin to get it? Not sure her resources are enough to defend her, should the Eldar choose to do something about it.
As a fluffy example, in a story I'm working on, L-C Aedan Qel-Drake is wowing one of the newer ladies on his ship, while she cleans his quarters. One of the two things there no one else touches is a sword, hanging on the back of his chair right then. When asked about it, he tells her of how he got into a fight with an Eldar vessel. He got away, but not undamaged. Later, he and that same ship both got jumped by Orks. The Eldar vessel agreed to aide, but fell in battle, before the Stellar Dragon managed to finish off the last bits of the Ork force. Not sure if the fight the two ships first had contributed to the Eldar ship's loss, but oh well. The Eldar crew were stranded, but the Captain was a female, and Aedan is incapable of leaving a woman, even a xenos, adrift. He brought the remaining Eldar aboard, under heavy guard, and put them up. A bit later, he got to talking with the Captain. She wasn't interested in him, much to his dismay, but appreciated not being left to die. She told him a place where they could go, and the Eldar would be retrieved. Against the advice of some aboard, he did this, and the Eldar came for their kin, actually not firing on the Dragon. As she was the last Eldar off the ship, she thanked Qel-Drake for his actions, and gave him her sword, as a payment for his trouble. It's served him well since then, and never let him fall prey to the weapons of his enemies, almost as if she's watching over him (though that thought might be heresy). It's a fun bit of fluff, and a cool way to get a good-quality Eldar Power Sword, other than killing a Corsair Captain on their bridge, but I don't know if the Eldar would. They tested each other in combat, fought together when necessary, he did save and spare her crew, didn't rob them, and on. Other than having to put up with the short-lived advances of a mon-keigh, it wasn't so terrible. Might she do this? The Eldar have more, and gear is never something they are in short supply of (just bodies to use them). Did Lady Charabelle have to have killed a Harlequin? How might she have purchased one of their weapons, otherwise? Not sure if she has the money to buy one from someone else who could kill one.
Okay, sorry for the long BS ramble. I now look forward to some ideas, some examples, and what have you. Thanks for sticking through it this far.