Honest answer?
Kitchen Sink (excluding AF).
2 INF Belo
2 INF, 1 ARM Balkans
2 INF, 1 ARM Eastern
1 INF, 1 ART Southern
2 ARM Germany
Ukraine liberated w/ (on average)
5 INF, 1 ART, 4 ARM, plus the seized AA gun.
Also send 1 INF Norway to Karelia, TRN 2 INF from Norway to Eastern, build a few ARM in Germany.
If USSR goes land units only to Ukraine (10 INF, 2 ART, 1 ARM), they CAN liberate Ukraine, on average w/ 1 ART, 1 ARM left, and with West Russia and Caucuses vacant of forces, leaving only the Moscow units and their R2 build for units on the board (and any Siberian forces working their way west).
If they use their FIGs, they have 1 or 2 INF, 2 ART, 1 ARM, and 1 or 2 FIGs left… they risk AA against both FIGs.
So…
USSR has 5 INF, 2 ART in Moscow. Archangel and West Russia are vacant (AA in WR). Germany has an INF in Karelia, 1 in Belo. 2-5 INF in Eastern, 2 more units that can be amphibed from Southern, and ARM from Germany. When Germany counters Ukraine again on G2, the Russians are out of offensive units… 1-2 FIG, and 2 ART (plus any builds). They are also out 1-6 IPC’s from a free SBR of either Caucuses or Moscow (no AA guns, they are in WR and the Germans took the one in Ukraine)
You can;t trade that heavy with Germany for ANY length of time. A single bad set of dice, and Russia is out income, and out an IC in Caucuses.
Also, if they ARE pulling their Siberian forces west to help out, Japan is doing a steady march through Siberia and China…
This also leaves the Luftwaffe and Baltic Fleet with nothing to do for a few turns except annoy the piss out of UK and interdicting any attempts by UK to land heavy to help Russia out to the north…
Oh, and Germany is also parading around Africa after winning in Egypt, unless UK countered in Egypt, in which case Japan is also advancing through India (Japan $40+ IPC’s on J2…)