Um, from what I have read about Stalin, it is very likely that either the Russian people would have eventually rebelled against Stalin and the Communists and that he would not have modernized and advanced the Red Army that he did, to the extent that he did, as fast as he did.
There's very little historical evidence to support that contention. What brought the communist system in Russian down eventually was its economic failure, deftly assisted from the West. There's almost nothing to indicate that a generalized rebellion against the Soviet system existed in the time span in question; indeed outside a limited circle, it's arguable that Stalin actually had a pretty good image in Russia as a whole. It was the old traditional "he's a good man but he's sometimes mislead by bad advisors". In that context, the Great Purges were seen as him getting rid of those bad advisors. Notably, those purges, drastic though they were, were limited to a relatively narrow circle.
The second part of your comment is odd because it doesn't actually relate to the first part and putting them in the same sentence defies logic. In point of fact, the Russian military establishment in the 1930s was extremely forward looking and advanced. It was experimenting (on a grand scale) with concepts that matched any in the world (mass use of paratroopers for example; the development of combined arms armor tactics at a time when most armies were either ignoring tanks completely or succumbing to the Fuller Heresy - or both, the integration of air support into ground operations and so on. In fact the social and operational ethos of the Soviet State in the early - mid 1930s was highly conducive to doctrinal development rather than the reverse.
IF this butterflies away the Winter War, then not only is the logistical side of still against the USSR too much for a conquest like in OTL but he would still have a less than optimal armor strategy.
I'm sorry but this also doesn't make much sense. The Winter War has absolutely nothing to do with the logistics of invading Russia from the west. That's a factor of geography, size and the orientation of railway lines. Neither factor has anything to do with the operational doctrines of the Soviet Army as they existed pre-Great Purge.
One of the main things that got Stalin to modernize the Red Army was its appaling performance against Finland and later the extreme pressure by the Nazis.
Actually, the problem is both simpler and more complex than that. During the 1930s, the Russians created an extermely modern and well-balanced army that had an excellent command structure. Stalin then effectively destroyed that Army in the Great Purges. What went to war in Finland was the derelict husk of that Army commanded by incompetent time-servers. Finland had nothing to do with the massive change in the Soviet Army that took place between 1937 and 1939. What it did do was catastrophically highlight the disastrous effects of that change. What the German assault in 1941 did was to reverse that change. It's not that common knowledge but there actually was a sort-of coup in Russia in October/November 1942. Zhukov and the other senior Russian generals went to Stalin and told him to his face that unless he allowed them to put the Army right and stopped interfering with the military command structure, they would walk off the job and Russia would lose the war. Stalin caved and from that point on, Unitary Command was restored. The Army that won the Second World War in 1943/44 was the Army Russia had in 1936 before it was emasculated in the Great Purge.
Had that Great Purge not happened, the army facing the Germans in 1941 would have been the 1936 Army but equipped with T34s and KV1s - in effect the Army Russia actually had in 1943/44. If the Winter War had actually happened, the Finns wouldn't be boasting about it today - or if they do, they'd be speaking in Russian while they did it. As Grazhdanin Stas has pointed out, logistic and industrial problems might well have meant that Army was not that effective outside Russia (although I believe he understates how effective it could have been) but inside Russia, the 1935/36 Army upgraded with 1942 equipment would have been a very hard nut for the German armies to chew upon. They'd have broken a lot of teeth trying.
Without a reason to look outward, he would most likely continue to focus his paranoia at home.
This is a non-sequiter of amazing proportions. Stalin was paranoid because everybody was out to get him and he knew it. His governmental system relied upon his enemies taking each other down for him while his government methodology was that of an elevator. Rightd ecisions and loyalty to Stalin took one from the lowest floor to the highest with remarkable speed but screwing up or suspected disloyalty could drop one down again with equal speed. In political terms, Stalin knew that Germany was coming for him sooner or later, he had every reason to keep looking outwards.
What about the Soviet-Finnish War? That was basically: "We'd like you to redraw your boarders to our advantage." "No." *Invades*
It was a lot more complicated than that and the Finns were a lot less innocent than post-war propaganda has alleged but Finland really stands out because it was an exception to the general rule. For example, after the clashes with the Japanese, the Russians didn't head south in a massive territorial grab even though they knew they comprehensively outclassed the Japanese across the board. Likewise in Eastern Europe, the abiding impression is one of the dog that didn't bark. The 1930s weren't marked by any "minor border readjustments" even though the scope for them existed.
I wouldn't say that the German's didn't understand the Soviet war production capacity necessarily, having cooperated with them from 1922-1932, rather the assumption was that a massive shock a la Barbarossa would overwhelm what the Soviets had available for production, negating any possible advantages. Of course things didn't turn out that way.
Frankly, I don't think the Germans had a clue what Russia was really like or the resources it could command. Having cooperated with them between 1922 and 1932 didn't mean the Germans saw anything and everything. That would be profoundly un-Russian. The Germans saw an image that was carefully presented to them and the "cooperation" was carefully controlled to match that image. It's called Maskirovka - strategic deception - and the Russians are surpassingly good at it. The Germans used their 1922-32 experience to estimate the size of the Russian Army and came up with a figure that was 50 percent of the real number. They also underestimated how quickly the Russians could form and mobilize new units. Neither of those errors was an accident.
In Germany the effect would be next to nil. The left tried such a powergrap already in 1919 and a few years later they tried to take control of the Ruhr valley. In both cases they were dispersed without many problems. Germans are notoriously bad at revolutions.
In Germany, perhaps. But in France (then apparently the most capable military power in Europe) the communists were a major political power that was very close to gaining control. Italy and Britain were in a similar position - it was the strength of communist-dominated factions in the UK that led Halifax to espouse the beliefs that he did. A "European Alliance" that has Britain, France and Italy hobbled at best and out of it at worst isn't very impressive. A s time wore on and the true nature of the Nazi regime became apparent, its very easy to see many of the more powerful European countries dropping away.