Honestly, with this, I’d say dig into existing settings and see what they’ve used.
Warhammer 40k comes to mind. The setting dials itself up to parody, but a lot of it underlying logic is actually surprisingly well thought out, and there are a lot of bits you can take inspiration from.
The quality of the tie-in books waffles pretty wildly between completely unreadable and some of the best tie-in fiction I’ve ever read. The Caiaphas Cain novels (by Sandy Mitchell) are a pretty good introduction to the setting, and should give you some ideas. I’m not a huge fan, but Dan Abnettt’s Eisenhorn novels are also a good look at the setting, though you might need to do some outside referencing on a 40k wiki.
The tabletop game itself is expensive as hell to get into, but, you should be able to find some of the army codices cheaply in used bookstores. Those should give you some ideas of what you could outfit your characters with.
As a bonus, 40k does have some fairly good justifications for melee weapons in a distant future setting. That said it is supposed to be a Dark Age fantasy world in space. And there’s a lot of material you’ll probably want to filter out; it IS still a fantasy setting, psykers are Mages, Eldar are Elves, Necrons are Undead, Daemons are demons, and Orks are… well, Orcs. But it could still be useful for giving you ideas.
I’d also recommend looking at GURPS. GURPS isn’t a conventional RPG, so much as it’s a toolbox for the GM, and while I’ve never been a fan of the system itself, the research that goes into the average GURPS book, makes them invaluable research tools. I’m not sure if Space, Ultra-Tech, or High-Tech is the book most suited to what you’re doing, but if you can find any of those used, you’ll should have some top notch material to work with.