About Starsector mods, the ones I played:
- Ironclads - a total conversion, with 4 solid factions + some pirates + space alliens, all with their own weapons and style, and with complete new galaxy, where each faction has its own territory and systems with various roles affecting faction economy
- Exerelin - it includes a faction pack with like 15 factions that can be disabled individually and adds faction behavior such as diplomacy, gethering resources, sending fleets at enemy factions, and capturing bases. The galaxy map is randomly generated and the gameplay is quite sandbox.
My knowledge about these mods may be a little outdated as I haven't played Starsector seriously for a year.
I was actually a contributor to Exerelin for some time two years ago (mostly some minor bugfixes and tweaks).
Now after looking at Starsector forum I see Exerelin is being continued as Nexerelin and it is modded by... @KingRaptor aka Histidine. The internet is too small lol.