I'd guess the Nexus population pre-revolt was probably somewhere in the range of 1500-2000 people, with barely enough supplies for only a few months. Construction, station security, medical, and administration primarily, with most of the rebellion being construction and station security. The Krogan complement probably wasn't particularly sizable, but with Krogan it doesn't necessarily have to be, so long as the Krogan are central to any choke point. We can reasonably assume a third of the station population, plus the Krogan, didn't rebel, so even with numbers on their side the resultant exiles still would've lost.
I'd guess the total population of exiled would be in the 700-900 range. Pile on another 90-150 Krogan who left for Elaaden after Spender and Tann * 'em over. With about a third of the population, if this is the point where they attempted colonization of Eos on their own, they then lose another 5-10% to Eos, 80% go back into cryo, and a skeleton crew of administrators, a core science/medical team, security (who form the station militia) and construction are barely able to keep things from completely falling apart for a year before the Hyperion shows up.
Note I'm assuming roughly a 20% casualty rate for the rebels assuming a broken command structure and an "every man for himself" attitude versus a 10% casualty rate for the loyalists, due to the participation of the Krogan, and the loyalist militia being composed mostly of Turians (where we're assuming they're nearly all ex-military).
And yeah, this is all wild mass-guessing on my part.