If you put 1 on Soviet Far East, Japan has a high percentage attack there with inf/artillery. The lone Russian infantry dies, the territory is lost, and if Russia counters SFE on R2 (Russia’s second turn), on J2, Japan just takes it right back and kills Russian infantry. Russia trying to trade early game with Japan and Germany is just not something that Russia can sustain at all, with 3 territories against Germany and 1-2 territories against Japan, and only 2 Russian fighters to work with.
And no, it isn’t "easy to do if I just buy a third Russian fighter’, because a German tank push drains Russia out pretty fast when combined with Russia sending units east. Less Russian ground units (buying fighter) plus less Russian ground units (sending units east) equals German push in Europe.
Stack Yakut? I wouldn’t. I don’t want to trade with Japan on the coast anyways. So it’s back towards Russia. It is not in Russia’s best interest to lose unit for unit against Japan in an area in which Japan can see everything coming and respond instantly. Specifically, Russia has to march infantry into Novosibirsk then into Yakut, before they can threaten Soviet Far East or Buryatia, which uses up a lot of time (production one turn, then march, march, fight, for a three turn delay, as opposed to a one turn delay of production-fight from Caucasus into Ukraine, or production-march-fight of two turn delay from Russia to West Russia to Belorussia/Karelia.) Also Japan can see it all coming, and can easily stack so heavily that Russia is forced to retreat, losing more time, or Japan can divert through China, forcing Russian retreat again (and losing time again).
6, 1, or none on Buryatia, and that is all. I’d say none, unless you’re trying some sort of KJF (Kill Japan First) variant, or willing to risk a G2 tank blitz through Africa, in which case 6 is worth thinking about.
Why none? Why not one?
If Japan keeps its battleship at the sea zone east of Japan, a transport can offload two ground units plus battleship support shot for a high odds attack on Buryatia, which would kill one Russian infantry anyways.
Why not six?
Japan can hit Buryatia with up to 4 ground units plus air and a battleship support shot. Even if Japan loses, Russia will lose a lot of infantry that it can’t replace. So long as Japan retreats its air, it should be fine. If Japan wins, it’s very nasty for Russia, of course.
You can preserve the Buryatia stack by using the UK India fighter to hit the Kwangtung transport and land on Buryatia. But you have to make the decision on R1 whether to stack Buryatia with six or none. Suppose Germany gets lucky at Anglo-Egypt and keeps 3 German ground units there. UK will probably have to use 3 infantry, fighter, and cruiser shot for decent odds there, meaning the UK fighter can’t land on Buryatia. Of course, if Germany only has 1 ground unit surviving at Anglo-Egypt, then UK will be fine with just 3 infantry and a cruiser shot, but there’s no way to tell on R1 what will happen on G1.
Suppose that the Allies are willing to take a chance. IF Germany does not hit Anglo-Egypt at all, or IF Germany does not keep a lot of units at Anglo-Egypt, or IF UK locks itself into committing only 3 infantry 1 cruiser shot, or IF UK decides to hit Anglo-Egypt and abandons Buryatia hoping that Japan MAY not hit Buryatia . . . if, if, if. But consider that of Japan’s starting units, it may choose to send 1 fighter 1 bomber to Hawaii (along with some navy), and 1-2 fighters to China, leaving 3-4 fighters to hit other targets. 3 infantry 1 artillery and 3-4 fighters 1 battleship support shot has decent odds of destroying the Buryatia stack of 6 lone infantry. Of course . . . with the UK fighter, it’s a bit different. So it’s pretty much a question of risking a G2 tank blitz through Africa in exchange for helping protect the Buryatia stack.
Which is not to say that a Buryatia stack is “wrong”. I just don’t think it’s definitely “right” - i.e. it’s not something that I would say Russia should always always do. I think it’s a matter of preference.
Why not none? Because then Japan can just walk in with one infantry, and use its Japanese transport to land units at French Indochina, possibly setting itself up for a 4 transport J1 build, early attack on Africa, and early control of India. So there’s really something to be said for all sides.