I’ve found the best defense in slowing Japan down is simply fighting a slow, retreating battle towards Moscow/ Novosibirsk and then taking them on as Russia. Quite naturally, this means that by J4 or J5 you need to have MASSIVE allied help in taking on Germany.
Taking up this point, let’s look at the following: as has been said several times on this board, throwing an IC down in India is like giving Japan a free IC on the mainland. The Asian Wall strat… well, it’s been debated but really the Allies can only put 5 units down per turn while the Japanese can overwhelm both of those ICs in turn by pumping troops from the mainland with adequate transports. The best thing to do, as Russia, is to fighting the delaying battle and let Japan take what it will take inevitably but at the same time not losing the bulk of the forces you start out with in the east.
Put simply, if the Allies by turn 5 or so are still relying on Russia to take on the majority of the German forces and are not in positions to cause Germany to shift focus west, Russia is in SERIOUS trouble. If, however, the US has retaken Africa/ is pumping troops towards Europe and taken out the German navy and the UK is pumping troops into Russia via the northern route, Russia SHOULD be able to shift some forces east and, with some offensive units that hopefully have been bought over time, will be able to strafe any Japanese columns heading there. Japan can take a lot of territory quickly but it cannot bring around the necessary offensive forces to really overwhelm Russia for a several turns because they need to march them west from either the coast (debarked from Japan to Manchuria/ Kwang/ FIC) or from any land based ICs.
I’m not a huge fan of the IC in South Africa… I’d rather re-take Africa (if I even lost it in the first place, such as Germany pumps troops in after retaking Egypt with Indian forces, and if Germany is willing to pump troops into Africa well that’s less for Russia) with American forces.