<Snipped quote by Wernher>Anywhere from 30 million to 90 million.
Whichever makes it fit for your nation(s) in comparison to the "big players" in size.
I'm iffy about that. I'll ender wiggin a little here and refer wikipedia for 1914 euro population.
Germany 56,000,000
France 38,000,000
Italy 32,000,000
Spain 20,750,000
Total 146,750,000
In comparison, Russia proper had 67,500,000.
Here, NOT!Russia PRK has 267,110,000
And I also have you, which is in the hundred of millions (Note, I don't know where your population is. Is it all in the mainland, or is it in colonies?)
I think 150 million is reasonable, considering the problems my nation face (Overpopulation, complete lack of resources)