A space station full of prisoners (plot explaining why everyone kills eachother) crashes with everyone onboard thrown into the depths of space with nothing but a hammer and a wrench and whatever you give them.
the build would be in space (obviously) with the various locations revolving around asteroids, broken down station parts, and (possibly) the heavily fortified ship that crashed into your station, full of NPC's with guns and loot aplenty
atleast, that'd be my idea in your shoes. Plus, it fits in with the energy generation theme if you're doing something futuristic.
On a more build-functionality suggestion, energy should be produced by solar panels or some kind of reactor generator if you aren't a sun hugging hippy, though I don't know how it'd work.
loot spawns randomly, but more dangerous areas having good loot with more weight (in spawning terms)
if by gathering you mean brick gathering, I'd suggest something like using money to buy bricks and basic machines, as if you did it the way salvage works, the map would easily get ruined really quickly if every brick can be broken, including weapon spawns.
Just my two cents on a similar idea I had.
