As I said, there would be a very small chance of Germany accepting an early eastern frontWoah! Why would the Germans want to push the Soviets before they were ready? And for Finland of all places?
As to the actual combat, I would like to see Finland have some NF's that develop a really prowerful set of defensive bonuses, so that as the Russians attack they will have a really hard time, but that the Finns shouldn't be able to roll them up.
Let the Finns grind the Russians down and perhaps the longer they hold on the more likely the Russians are to accept less demands/white peace.
The Winter War does start with a Russian NF so the Finns should defend with their own NFs.
I agree that Finland should be able to resist the USSR, but I don't know about capturing Moscow and kicking their Soviet butts to Kamchatka