Manpower does not matter anymore.
Cyber attacks, special forces, allies, resources, power projection, ability to succesfully occupy and stretch supply lines, hold a wide front, being or not being able to use your advantage (vehicles, drones, jets) through a mountain or across a river. Missile range, state of economy, morale of the military, training.
NATO just has to hold their ground and keep Russia surrounded. Russian navy can't go anywhere. They may invade rhe plains of eastern Europe but they're going to kill themselves trying to go through the Carpathians and, the Oder river.
Their supply lines will have to be very long, while getting harassed by the resistance, frontline will be wide, and they won't be able to make their tanks cross anyhing and western europe has great AA capabilities. Russia gets no air nor naval superiority, can't get their vehicles through a chain of mountains and through a large river. It may end up in a conflict of position similar to ww1 until Russia's economy collapses. NATO can seek natural resources outside of Russia aswell, easily. All it takes is modifying existing ports to receive it.
China getting involved? China is nobody's true ally. They profit and seize opportunities. Both NATO and Russia going to war, China can supply both sides and get ahead easily while laughing at us.
Once Russia starts to collapse economically. If the nuclear weapon hasn't been used already, it certainly will at this point. NATO fires back and the northern hemisphere is obliterated.
Russia can deal a lot of damage but it would most definitely collapse in an offensive war which NATO would force them to do. Russia needs to get closer to close the gap between the range of missiles, between NATO and Russian missiles (which are outdated, that explains why they took Crimea).
The last time a great power that seemed impossible to beat went against the world and the economic might of the US, it took time and casualties but they did not make it.