People more knowledgeable than I would know in more detail, but I think I know enough about the history of the Soviet Union and the general behavior of postwar Europe to guess at a few trends.
1. If Germany is a communist country first, it probably isn't a "Communist" country in the sense that we know the term, that is, it probably isn't arranged along Lennist Principles. As such, while the USSR will look to Germany for aide, there will eventually be some ideological squabbles between the two countries over which is closer to a communist ideal.
2. Communist Germany's leaders may dominate the international communist movement. The USSR won't be able to claim that all true leftists have to unequivocally support them, as they are now no longer the "first" communist nation.
3. The USSR will beg Germany for support during the civil war if Communist Germany is stable enough. Of course, due to the postwar condition of the country, I doubt Germany is going to be willing to become as heavily involved as Lenin would like.
4. This is going to cause a great deal of panic in other western nations. Russia caused a Red Scare on its own, and that country was something of a backwater in the eyes of Britain France and the United States. If a place like Germany becomes communist, you probably see a worse Red Scare.
Not sure where this plays out long term though. That largely depends on what the German leadership does.
Again I don't know how plausible a communist Germany actually is, or how close to the truth my guesses are. If I'm radically wrong. I apologize.