I've been doing some thinking about this, so here goes...
There are roughly 20-23 systems (excluing Sol).... now I'm assuming that around 10-15 have been fully colonised. Each of these systems probably has 2-3 habitated planets, excluding moons and installations.
Given Earths current population (5.5 billion rough), and the likelyhood of larger populations being suported in the future over similar sized areas, I'm assuming there are around 5 billion inhabitants on average for each planet (possibly much more).
At an average of 2.5 planets per system, this gives 5x2.5x15 = 187.5 billion. If you include fronteir worlds /systems, ships, and installations, this would mean the GTVa has a combined population (Terran Vasudan) of around 200 billion, probabaly more.
Assuming 1% of these people are willing, and able, to sign up to fight, this would give an armed force of 2 billion soldiers... taking into account planetary defence, this would give the fleet a couple of 10s of million soldiers at least.
And, it would indicate that the NTF had several million active combatants, based on their success against the GTVA.
Finally, given the likely rate of ships, top speed of Argos', hippocrates, etc at around 20m/s, and the likely capacity of refugee convoys, i would guess that at least 5 billion were killed in Capella. And also several million in the NTF / Shivan wars.
Also, it would indicate the Lucifer killed at least 10-12 billion with it's attack on Vasuda Prime, as it would be most heavily populated Vasudan planet.