I haven't decided how I'm going to work the specialize in fighting orks and dark eldar,
Regarding specialize in fighting orks do I think a larger than normal amount of flamer/melta weapons is a good idea, if you plan to actually make figures, maybe use Salamander parts with their hand flamers and such.
As for the part about "returning lost technology and stolen gear to the imperium" I'm working off the idea of plains indians taking war booty in the form of horses and the like and specifically making raids to steal horses. I'm going to portray this in three ways, 1. straight up taking war trophy's from important battles/enemies be they war gear or vehicles or parts there of, that are displayed in their fortress monestary and in their ships. 2. Their primary enemies are orks and dark eldar, both take trophies, so the idea would be to recover imperial tech from those like SM helmets, pauldrons ect. Secondly when it comes to Orks specifically they tend to intigrate and pervert imperial tech into their vechicles when they capture them or salvage wrecks. thus the idea with this being that the chapter recovers those parts, be they a Rhino's front plate, or the hull of a Lemon Russ tank, and purge them of any xenos tech, keeping any SM bits and returning any of the rest to the Adeptus Mechanicus. 3. Despite not being a fleet based chapter they make a point of trying to capture vs. destroy any Imperial based ships they encounter in combat, be that pirates, renigades or chaos based (as long as the ships aren't overly corupted aka demonicly possed or warp altered) some of these are then kept to be retrofitted as escorts or Strike Cruiser, the rest are handed over to the Adeptus Mechanicus to be properly cleansed before being returned to imperial service.
I can see this leading to a focus on hunting/attacking the above mentioned enemies. With the flipside that the Chapter is not known to help defend the Imperium’s holdings, and/or they have a tendency to ignore enemies that don't use/repurpose Imperial tech, like the Necrons or Tyranids, if enemies that do are near, even if the former would be the bigger threat.
Maybe they are closely allied to an AdMech group/subgroup/world?
Maybe they frequently partner with the Mechanicus in searching out archeotech, holy relics, and/or new sources of knowledge? This search/gather could be done to the point where these considerations outweigh other military factors.
Maybe they are more focused on capturing Important Imperial tech than taking out the enemy or taking out the enemy leader? Like, it's more important to capture and holding a looted baneblade than taking out the ork boss, or taking out the main force and lose the baneblade. They sweep in, capture the important ImpTech and then leave.