so first off, good job for jumping in with a challenging player like Rader! I think you are doing fine with specific things, just a couple of thoughts.
First, don't stress so much about China. Really look at what is there, if he takes it all, it really doesn't change the overall equation. So what he gets a few more HI, not so big a deal. He will free up some units but not as much as you might think because he will add lots of garrison requirements. So there will not be quite the numberless legions tramping through the co-prosperity sphere that you think. So the goal in China isn't 'winning' it is making him pay, either in time or losses. So he is blitzing, cool, let him. Just keep him honest with his siege forces.
Second, if you think he will hit Russia, prepare for it. Hole up some dudes in Vlad, but get most of them to the West (or do you say north on this map... or just up, or ??) where the MSR diverges from the border a bit. It is just too easy for him to cup off the coastal area and then you will feel sad

But if you move to more defensible terrain and dig in then moving into the Motherland will make HIM very sad

Really, you will get way more in the long term if he does beat the crap out of your Chinese guys (not very useful) and activates your Sovs (moderately useful). If you are ready for it and take some precautions to limit his ability to isolate and destroy lots of units in the initial rush you will have a fairly strong defense that will really tax him. And you have enough strength for little forays and raids that can sap him far more than China. So its all good!
Really, as the Allied player you just have to be sort of zen. someone once pointed out that the Japanese in the early war can go anywhere, but they can't go everywhere. So just ride it out and wait for things to settle down, he will not be strong everywhere, it just takes some time.