That's pretty much exactly what I had in mind, Irony. And Fniff gets political meddling element - your superiors are always looking for excuses to shut you down and tie you up in outrageous demands and red tape.
You'd start with a standard-issue small mothership, a handful of scout ships and a few medium ones, an army of the weakest, most cowardly cannon fodder (and some well-equipped troops of your own species) and their commanders, a small gene lab and engineering plant. You'll need to plop down Exploitation Modules to convert Earthling materials for your own use, but they could be found and attacked if you don't keep watch.
As the game goes along, you breed/construct new types of troops on your limited budget. You'll need more resources and biomass to feed them, of course. Fuel costs this region of the galaxy are outrageous, y'know. On the other hand, you get to create all the abominations against nature, science, or both you could ever want. You can also requisition additional ships and assets from home, but that just draws closer scrutiny from the politicians.
I thought you could have some traits which double as fatal flaws, chosen at start. 'Alien Atmosphere' (you can't breathe the air in this dump, but then, neither can they once you start terraforming it to normal), 'Networked' (the minds of the invaders are connected psychically or technologically - their leaders improve their skill on the field, but they also die or panic when a leader, including you, is killed), 'Isolated' (you're not bothered by politicians as much, but good luck getting anything from home), etc.