Instead of doing too much, it might be advisable to hit W Rus hard with 10 inf, 2 art, 3 arm, 2 ftr, and create deadzones all around and trade territories with Germany until the reinforcements arrive.
This is usually what I do, and with a 3 inf, 3 arm buy you immediately have 7 armor which should be close to matching Germany and should prevent a German move to either Kar or Ukr for several rds. You can follow up in rd 2 with 4 inf, 1 rt, 2 arm and your overall offensive units start to look pretty impressive: 3 rt, 9 arm, 2 ftrs.
