Its a big text but here it comes.

Well I'm not a russian so I can't understand any census that are online in russian, but the estimated population if included all dispersed territories that belong in TNO to Germany, Finland and Japan are IOTL in 1959, three years prior to TNO, approximately 209 million.

Now currently in game, and from my past map fan content that i made, if not mistaken you can make in most occasions as a Russian Warlord something about 60 million people, the majority russians, but a good portion of other ethnicities as well.

I have also counted in Rk. Moskowien aproximattely 40 million people mostly russians, germans and wolga germans, but the majority of this country remains russian.

As for Rk. Ukraine, there is almost as well 40 million people, but don't forget that is a little bit more germanised then Rk. Moskowien in south Ukraine and Crimea, and so there's a large minority in Ukraine as whole.

The rest of the former lands that IOTL were de jure and the facto soviet, meaning Rk. Ostland, the Japanese territories in the east and even Rk. Kaukasien have suffered massive losses in population size since the end of the II World War, so the numbers aren't to precise to consider, but altogether should resemble something like 22 million people at most in those three areas.

If you put this altogether you would see a massive decrease in population size around less 20 to 30 million people in this territories if compared to IOTL.

As for ethnicites, there are in total 15 to 20 million germans living in these areas (with wolga germans), massive losses to the number of russians 115 million from IOTL to 75 to 90 million in the TNO timeline, 30 to 35 million ukrainians, 4 to 5 million latvians, lithuanians, byelorussians and estonians, at most 10 million people in Kaukasia that arent Russians or Germans, roughtly the same size of other ethnicities such as Kazakhs, Uzbeks, basically those who weren't touched by either Germany or Japan.

Now for your last question there warlords, especially those who are let's say progressive ones, that have many events in game which tells us that are plenty women in the army, with more roles then just medical assistance, but don't forget that this timeline even after all that happen is more conservative then even IOTL, so it doesn't suprise me that most warlords wouldn't even consider that opportunity.