I suggested the same already, though the first contact war might be a bit short for a full campaign. As far as I remember the backstory, the Humans got completely wiped out in the actual first contact, then the Turians overwhelmed the orbital defense of Shanxi and when the alliance fleet turned up, the gave the Turians a beating.
With the exception of those three (more of less) big battles there wasn't any fighting in space, just ground actions.
I think the Skyllian Blitz would make a good setting or maybe the conflicts with the Geth heretics that happened before, during and after ME1.
