Great update. I have one question though.
Can there even theoretically be an alien empire on par technologically to any human empires or are any possible aliens only a cannon fodder in a humanities showdown?
This campaign is inspired by an old RPG called 2300AD. In that game, humanity was split into many factions and ran into a powerful alien empire. Eventually they had to unite to defeat it. About three years ago (game time) I added an alien empire that is just as powerful as any current human Empire and is already in one human system, although neither side knows. However, that is not intended to be the main bad guy.
Within the next year or two of game time I will be adding a very powerful alien race. I haven't decided on the theme yet but I am leaning towards a few fictional empires for inspiration
1) Galactic Empire from Star Wars
2) Imperium from WH40k, although with aliens not humans.
3) Kafers from 2300AD
4) Cylons
5) Dilgar from Bablyon 5
etc.
Any other suggestions welcome. I'm not looking to build exact copies but use them as inspiration for a large, very powerful enemy.