I wouldn't think its a massive amount if you're limiting it to Strana Mechty it doesn't even have the largest space station in the Clan space. I'd say 2-3 million at most and thats a lot
Taking 2,000,000 in 2800 and applying the 2.1% growth rate gives you a population of more than 360 millions people in 3050.
I went the other way around.
Since I have an estimation of the Clan population in 3060 with also a 3050 estimate, I decided to get back to the population of each planet and saw I was missing a lot of people (circa 400,000,000).
Assuming that the absorbed Clans are just that, ie part of other Clans and getting back to my estimate of Clan Nova Cat and Clan Ghost Bear, I found out that in 3060, there could be something around 218,700,000 Free Guilders and 176,900,000 in 3050, which would make them the most numerous part of the Clans.
However, this is assuming that in my files, they are assigned to one Clan or another (otherwise I would have a problem and I would need to redo all the maths).