Could this lead to the participation of China with Russia annexing Manchuria and others following suit? What would be the long term consequences?
It would be bad for Russia. A Russian victory in the War would mean a greater integration of Manchuria into the Russian Empire - with all of its Chinese population. Today the combined population of the three provinces of Manchuria are nearly the same as Russia's (though admittedly, in this TL the population will be somewhat smaller as Russian Manchuria is hardly likely to industrialize at the same pace, assuming Russian possession throughout the 20thC). Still, this means that the Russian Far East becomes Chinese, not Russian - no Russian action save genocide can reverse that.
Russia is unlikely to get any benefit from defeating an Asian power. The shock of 1905 was that a
white European power was trashed by an Asian one in conventional war - if Russia had won, it would be considered in the natural order of things. Russia didn't get a lot of kudos either for defeating the Ottomans in 1878, Moltke saying that it was like 'the one-eyed beating the blind'.
Indeed, without the shock of loss, Russia's military weakness becomes even more pronounced than OTL, which would serve it poorly in the upcoming Great War in Europe.
On the other hand, Russia's victory does mean that the Tsar doesn't lose face before the Russian people. Victory-fervor should ward off the 1905 Revolution, maybe give the monarchy some more time for a gradual political evolution. However, again without the shock of defeat Russia might not even think about such reform - which only builds up more social pressure that will eventually explode in Nicholas' face.
Russian ascendancy in the Asian northeast will probably result in an accelerated colony-grab within the Qing Empire as countries balance out increasing Russian influence in the region. Anglo-Russian relations will be more strained as a result (though the threat of Germany will still bring them together).
Depending on Japan's performance during the war (a 'valiant' struggle against Russia will still earn it points) a defeat might not actually hurt it that much and for resource reasons alone it will have to accelerate its acquisitions in China, maybe in its 'sphere of influence' in Fujian. A catastrophic failure against Russia on the other hand i.e. resulting in the loss of Korea, will spell quite a bit of danger for the Japanese ruling elite, especially from the nascent anarcho-syndicalist movement.