18 IPCs is well within the range of “normal” bids for the Allies in 1942.2. So there’s nothing crazy about giving Russia 6 extra infantry. The question is whether that pushes your game in an interesting direction. With more infantry, Russia will be able to hold out longer against German/Japanese attacks, and they may have some more flexibility to purchase some tanks or fighters, on turn 3 or 4. Russia would still want to make conservative purchases (infantry + artillery) on turns 1 and 2 because it will take some time to gather those extra 6 infantry and march them over to the front lines.
With no bid and less-than-heroic support from the US/UK, Moscow often falls around turn 6 in this game. So your “swarm of infantry” rule would keep Moscow alive for an extra couple of turns, maybe until turn 8 or so. Meanwhile, the western allies are still going to have a very hard time in the Middle East and in the Pacific. Egypt will usually fall on round 1, the US Atlantic fleet will almost always fall on round 1, the bulk of the US Pacific fleet will usually fall on round 1, the British Pacific ships will usually be dead by turn 2 or 3, China will usually be dead by turn 2 or 3, and India will often fall on round 4. Can the western allies rebound from these “predictable setbacks,” build a dominant fleet, build an adequate pipeline of loaded transports, and seize enough key territories to balance the loss of Moscow, all by the end of turn 8? Typically this means conquering either (France + Italy) or (Philippines + Borneo + East Indies + Kwangtung). Anything less, and the Axis will be able to take the income they get from looting Moscow, turn their tanks around, and drive the Allies back into the sea on turn 11 or 12, seizing a permanent economic advantage that will ultimately end in Allied defeat.
Does that sound like an interesting challenge for your play group? If so, give your bid a try. If not, maybe try a different bid. There’s nothing ahistorical about a Russian bomber corps in 1942 – the Soviet Union manufactured tens of thousands of modern bombers in every year of the war, and actually had quite a large air force for the era. The Russian navy was smaller, but still played a significant role in operations in the Baltic (preventing the German navy from re-supplying the Siege of Leningrad by sea) and the Black Sea (evacuating tens of thousands of Soviet soldiers from encircled positions in Ukraine and safely withdrawing them to the successful defense of Stalingrad).