How many? One thousand? Two thousand? According to the 2010 census there were 2446 ethnic Chinese individuals, right behind 4192 Koreans. Let's suppose it's 5000 now. It would still be less than 1%

All this talk about taking over Russian territory is just pure fantasy. Russia, on a liberal / anti-imperialist wave, even in a bankrupt, extremely weakened state could only become kind enough to detach Yakutia, Caucasus, and some other distinctly ethnically different autonomous regions, but it won't allow anything to happen to the ethnically Russian regions, nor these regions themselves could imaginably see themselves separate. Russia would still be a nuclear power, and I doubt the Chinese would risk a world apocalypse for a piece of tundra.