What were Stalin's goals in Eastern Europe?
I would say that one of Stalin's primary goals was to create a buffer of nations to prevent any hope of attack from the West. Since the turn of the century, Russian history had been filled with examples of dealing with challenges from Europe. From fighting in World War I which descended from fighting in Western and Eastern Europe the challenges of World War II when Hitler invaded Poland and set sights on Russia after unifying all of Europe, Stalin sought to put an end to this by taking over a chunk of nations in Eastern Europe and ensuring that Russia would be insulated. Stalin either installed Soviet- friendly governments or outwardly overtook the nations in order to maintain his own buffer of nations that could prevent a takeover or advance from the West.
In my opinion, Stalin's main goal in Eastern Europe was to create a buffer zone that would protect the Soviet Union from the West.
I suppose some people would say that Stalin wanted most to spread communism, since that is what communists are supposed to do. But I think that Stalin was really more interested in creating space between the enemies in the west and Russia.
Russia had been endangered by invasions from the west in 1812 and in 1941. Both times, the size of Russia saved them. Stalin wanted to have even more space so that it would be that much harder for enemies to invade from the west.