But in the long run, Germany, and the rest of Europe itself, would face the Soviet invasion in later years. Stalin was preparing for the conquest, there is no doubt about it. When you see the scale of industrialization, weapons production (the type of weapons) and military installations it is clear what the end goal for Soviet Union was.
Worth noting is that Sudetenland was German by population but the rest of Czechoslovakia was not. If Hitler took Sudetenland and not the rest of Czechoslovakia, there might have been a possibility for an agreement between Poland and Germany about the Danzig corridor. But when Germany took non-German region, the mask fell. So who knows.
I agree with virtually everything you said above. I would go further and say I think that without Germany fighting against France and UK, a Soviet invasion of Europe becomes much less likely. If the Soviet Union didn't make a M-R Pact with Germany, but still moved unilaterally against Finland or the Baltic States, the Communists probably would've faced a unified Europe.
As far as economy goes, Germany had a lot of options. Whole eastern and south-eastern Europe depended heavily on German tech while providing Germany with raw resources. Countries like Yugoslavia, Romania and Turkey provided a lot of raw materials, and we also have Soviet Union that was very happy to buy any and all German tech and machines for resources. So economy would be fine - there was a market for everything Germany would make. Western nations had colonies anyway.
I tend to disagree with what you're saying here. From an international relations standpoint, the Czechslovak partition was a catastrophe which gave Hitler had significantly fewer and worse options until he went to war. Until the French were defeated by Germany, Romania actually sold much more oil to the United Kingdom than Germany. And Turkey and Yugoslavia, ostensibly neutral, were closely aligned with the Allies.
Adam Tooze describes Germany's 1939 Balkan resource-trade outlook:
So long as the Allies have a presence on the continent of Europe, in the form of France, the ability of Germany to monopolize power in the Balkans is severely limited.
One more thing to widen the perspective, Romania is a big producer of oil by European standards, but Romania only produced about the same amount of oil as the US state of Ohio, which was merely the 16th highest oil producing state in the USA.
And there is for Germany the option to trade with the USSR. The trade that historically the USSR insisted on was for Machine tools for Russian raw materials. This had the effect of making Germany stronger in the short-term, but it also definitely made the USSR much stronger in the long term. It's not a good option for Germany long-term unless the USSR is being played by a friendly human.