Sounds like you are looking at a J3 attack on the western allies, allowing you to crush China first. Didn’t mention what buys you will be making, but most would probably buy 3 transports (maybe buy a mech, or save the rest), or 2 transports and a minor IC for the Chinese coast J1. You will need lots of transports as Japan
If the Russians stack Amur w/18 inf and 2 AA on R1 I would hit it with everything that can reach on Japans first turn (including transported units and lots of air power). Eliminate the threat, and help out your German ally. This will allow you to blitz across the tundra cutting down the Russian income as well. Don’t be too worried about the 6 Russian units that will pop up because of the Mongolian rules, they are easy enough to round up (that’s why you might want to buy a mech J1)
**Side note, if the Russians move everything to Sakha on the first turn then you should take Amur with all units that can reach (including some transported units w/tank from Japan). You now have the Russians trapped and will be able to hit them on your next turn (make sure your air units will be in range).
We normally see the Russians back peddle on R1 though, and start heading the bulk of those units towards Moscow leaving maybe 6 inf and AA behind just to keep the Japanese honest and from blitzing the back-lands w/tanks. If they do this then they are probably thinking about a fighting retreat, or maybe a stalemate depending on what you throw at them (or if you will honor the NAP Mongolia thing).
As far as kamikaze, use them if you get the chance. This is a defensive thing though so you can only use it when the allies attack you in one of those zones.