I think it is reasonable to think Stalin would expand through military means when he were capable and when it was convenient. He was almost certainly buying time until he could invade Germany. After that, and then the capitalist-democracys in Europe.
It kind of sounds as hollow as Nasser in the 6 days war. I think the arab socialists, as with the stalinists in Russia, were using the talk of being on the defensive for tactical reasons. They were every bit as ideologically agressive as the Nazis and I have no reason to think this wouldnt tanslate to invasion.
Without a doubt. The Soviets were merely biding their time; they expended a lot on fomenting domestic unrest and sabotage until they felt strong enough to launch military conquests. Hitler just happened to jump first against Stalin, is the only difference in that timeline.
As for the 'they started it!' narratives, military and defense doctrines left the schoolyard excuses behind hundreds of years ago; attacking first is indeed considered to be a justifiable defensive move in the face of coming aggression from a moralist view. Only idiots would let their enemies get off the first shot these days.