I feel like buying slow movers round 1 (6 art 2 inf) and then buying fast movers turn 2-4 then buying planes after works wonders, since the slow movers end up at Moscow G6, and the tanks/mechs are supporting those artillery at Moscow’s doorstep, though G4 purchase of mechs will make it G7. Strafing Yugoslavia with your German troops will make seizing Ukraine G3 easy with a G2 DOW. Basically, just make a beeline for Moscow, moving small groups of units to take other territories while leaving the vast majority of your forces to take Moscow by G6.
G1: 6 ART / 2 INF (could also do 4 ART / 2 INF / 1 Destroyer to kill the Russian submarines)
G2: 10 ARM / 2 MECH
G3: 6 ARM / 4 MECH
G4+ any mix of infantry to defend the western front and planes to move to the East would work, depending on what the Allies do you could plop 20 infantry a turn in the west or build a crap ton of planes to go to Moscow. All of the G1-3 purchases will make it to Moscow right before the Siberian infantry will arrive on R6. If you have the Ukraine factory you could buy 3 mechs or 3 tanks a turn there since they are only 2 spaces away from Moscow, or G4 you could put 3 infantry or 3 artillery there since they will be able to make it G6. But basically invest most if not all of your money to the Eastern front for the first 3 turns and then focus on defending the West from the Americans and British.
Once Moscow is taken then you can use the remaining Germans to take out the Caucuses, Leningrad, Stalingrad, and the Middle East. Germany should be making a crap ton of IPCs by that time and that should be plenty enough to shut down the Allies in the West, unless the US is investing 60+ IPCs a turn in ground units to land in Spain, Italy, or your coast.