Stalin would go and alter your previous post in an armor change discussion thread behind your back, making you look like a total moron, then laugh about you to his other friends about how cool he is and what he can get away with on his website. Then the thread would devolve into a shouting match between Churchill and Hitler with Stalin laughing on in the background the entire time.
OH WAIT where were we? Defending Russia? Yes… Just build ART R1, then ARM after that with INF sprinkled in. Try to keep your tank stack alive, retreat from battles before you leave a stack of THREES (now that we know tanks can still defend with 3s) out there vulnerable to a counterattack. Don’t be afraid to push the offensive, especially if Germany pursues a large fleet/Med. adventures/Sealion. You’ve got the advantage in unit counts as long as the dice don’t swing terribly far; try not to leave medium INF stacks exposed if you can help it, they’re terribly vulnerable to getting diced in battles without armor/FIGs to back them up. Capture the initative and make the Germans respond to YOU, don’t be the pushover player who just builds INF the entire game and waits for the end in Moscow.