A 7-doom-ray ship(154atk) would be an 8-blackhole-eruptor(200atk) ship if your willing to put in the(ton of) extra research that missiles take. Anyway, back on topic...
"2. GalCiv2 has a certain level of abstraction, among which is also the abstraction that the space and money a weapon system requires also includes the power source for it."
Yes. The technology description for HyperWarp 2 says that it takes considerably less energy to make ships move as fast as the original HyperWarp could achieve - and in the ShipYard, this translates into the HyperWarp 2 engine being 'smaller' than the original HyperWarp engine even though it's visibly larger if you look at plain physical size.
Similarly, the Nano Ripper is 'larger' and costlier than Singularity Driver 4 - yet they use the same tech. But Nano Ripper simply uses a lot more power - expressed in it's size and cost - to deliver 2.5x the smash of the frugal Singularity Driver, Mk.4.
there was a feed a while ago about civilian ships
i still think that is a good idea to have civilian ships running around to
Yes, I think so too. Maybe tiny cruise ships that randomly travel from planets to influencer starbases and foreign planets(representing tourism), and tiny cargo ships doing the same in case of economy and mining starbases(but not affecting their bonuses).
Maybe we could also have planetary improvements affect a planet's orbit. Like a Zero-G Sports Arena on a planet would result in tiny, brightly colored racers zipping around planet orbits, but in very wide orbits to avoid orbiting warships and moons. And building the Orbital Terraformer should actually result in a terraforming ship appearing in the orbits of planets. And Military Starbases could actually have tiny Fighter Drones buzzing in and out of their big hangar-pyramid central structures.
All these ships wouldn't be attackable, except in the case of Pirates - the Pirate attacks on civilian ships wouldn't be physically visible or have any effects on production, but would result in some small morale drop that gets worse and worse until those Pirates leave the sector or get destroyed.