Okay with all of that given and the Chaplians being a thing....
[ ] Librarians: The Chapters Librarians are particularly well trained and have far greater resistance to the temptations of the warp.
[ ] Blademasters: The Chapters Marines have honed their skills with the blade and are among the finest swordsmen in the Imperium.
[ ] Marksmen: Even among Space Marines the marksmanship of the Chapter is top of the line.
[ ] Chaplains: The chapter has more and higher quality Chaplains than average among its numbers.
[ ] Scout Training: The Chapters Marines are given more advanced training in the art of scouting and as a result more of its Marines remain as dedicated scouts even after being promoted from the rank of Scout Marine proper.
I think its in our best interest for one of these. Librarians as said before would pair very well with the Biomancy they got from their homeworld, the Chaplains are more for trying to make sure this chapter does NOT fuck around and turn traitor again trading performance boost for the training for safety net, I think Blademasters might be overfocusing and overspecializing on it but maybe worth it, while Marksmen would give them the ranged option and paired well with Specialist ammo as we really can't give any good equipment here for them. Scout Marines would be helpful in their job to gather intelligence or staying on their toes with it.
Yah on second thought the homeworld trait this chapter got was MELEE MASTERY and they are trained/mastered 'all forms of close ranged combat' including swords, so yah Blademasters are just to make them have a claim to fame to have the bestest Space Marines Swordmaster, I don't think we should got Blademaster.
[ ] Specialist Ammo: The Chapter has a ready source of specialized bolter rounds letting them bring the best possible ammunition for any engagement.
[ ] Extra Thunderhawks: The Chapter has access to additional Thunderhawks.
Honestly not much here, I do think specialists ammo would be good even if they didn't get marksmen training because you don't NEED a gun to use ammo. Take a look at IED or Vietnam traps using bullet. Just have an Incendiary and slip it into a box, gift, vehicle, or the like. I think that would be the best use of equipment.
Thunder hawks for moving Marines but even then It pales in comparison of the ammo.