it seems clear it was for their oil reserves to be able to sustain and expand their motorized force.

Hitler had very secure oil reserves due to the great dual-dependency of the USSR and Germany. The Soviets were voluntarily delivering all the oil the Germans needed and more, whereas the Germans in return brought to the USSR surplus amounts of refined metals, mostly steel. The two countries signed two Commercial Agreements in the timeframe of 1939 and 1940. The economic relations between the two countries were as healthy as the relations of any two inherently ideologically opposed mass-murdering regimes could have possibly been.

his descision not to attack Moscow, instead going for Stalingrad and the caucasus.

I do agree that the decision of attacking Stalingrad is not at the core of the eventual failure (which was however inevitable from the start just on the account of resources). The blunder lies in Hitler taking control from the "Prussian style" of warfare that his generals were proposing, wherein major urban and industrial centers would be captured to primarily hurt enemy short-term morale and long-term sustainability, whereas the Hitlerian approach, very "Darwinistic" down to its core if you will, was more aimed at natural resources, with immediate effect on sustainability but little at best effect on morale of the enemy force. The discussion which of these military ideas is more capable of providing success is perhaps beyond the scope of the question, but changing between the two schools is what made both of them fail.

It also seems like the Germans would've had to shrink their motorized force to be able to supply occupied France with energy unless they found a source besides their coal to fuel synthesis.

Again, the fuel and raw oil supplied by the USSR and Romania was plenty. Not once during the 1940 campaign had the Germans logistical problems beyond a very constrained local setting. Mismanagement of commanders or bureaucratic blunder was not impossible, but the fuel itself was always safely stored and ready in German supply depots - delivered by the willing Soviet partner. Only when the war against the USSR begins do we begin to see the massive logistical problems on the eastern front and in North Africa (even though both fronts had varying reason for the fuel shortage).

So it looks like a smart move to try and secure oil from the USSR as the Germans outnumbered the Soviet forces on the Eastern front and the soviets only had sizeable numbers of outdated light tanks (it was some crazy number like 22,000?) while their heavy and medium tanks in 1941 only numbered around 1000.

It is indeed somewhat reasonable to assume that the Germans would have had to deal with the Soviet threat at some point, but doing so while still at war with the British was another blunder. It made easy friends of the Soviets and, critically, the United States. 14,000 planes, 7,000 tanks, 8,200 anti-aircraft guns, more than 120,000 machine guns, over 300 warships, 15 million pairs of boots. Add to that 4 million tons of food and 2.5 million tons of steel (replacing what the Soviets had needed the Germans for, whereas the Germans couldn't replace what the Soviets had provided them). All of that would have been harder to sell to the American public had the UK already fallen to German influence.

In fact, I would argue that the 38 divisions the Germans kept in the west in fear of an allied counterattack, as well as 12 divisions in Norway and another 10 in North Africa, Denmark and the Balkans could have been somewhat helpful to the other 145 divisions actually part of the attack. Out of the 205 overall divisions, the Germans simply weren't able to deploy 60 - that's just short of 30% of the German forces. Quite the gamble indeed.

Expanding on your point though, it is true that the Axis Powers attacked with a numerically superior initial force, at 3.8 vs 2.8 million men. However, your dismissive stance towards Soviet tanks for one conveniently overlooks that the German tanks were also far from the wonderworks of engineering that contemporary wehraboos often make them out to be, and that both the Panther and the Tiger - the German tanks often so famed for the wonders they supposedly worked - were yet to be invented, and that they would be invented in direct reaction to Soviet advances in armored technology, especially the T-34. In fact, the T-34, which had been in production from 1940 onwards and had been at least been heard of by the Germans before the start of Barbarossa (the two countries shared military secrets), hopelessly outclassed Panzers 1 through 4 as well as Panzers 35 and 38 - which basically amounted to the entire German panzer force.

Even assuming that the T-24 and T-28 were the vast majority of Soviet tanks (an assumption at least somewhat reasonable, as reliable Soviet war statistics are hard to come by), you still have an initial Soviet tank force of 11,000 vehicles versus about 3,500 deployed by the Axis forces. So the Axis were knowingly taking on a foe that had the best model of tank available to either nation in ever-increasing numbers and that even when taking their smaller models far outnumbered the German ones.

The soviet army was very fresh as Stalin had been rapidly expanding the army, which would make it seem like a quick victory in 2 months would be possible.

I am sorry, but you might seriously underestimate just how vast the Soviet Union's territory was. Any two-month-victory assumption would assume not only outlandish military failure on the Soviet part (which one admittedly saw during the early months of the campaign), but also a cowardice on the part of Soviet leadership and the Soviet soldiers that only someone convinced of Slavic inferiority could really explain to themselves. It might have appeared reasonable to Hitler to assume that kicking in the door would be enough to bring the USSR down, but the German leadership at the time and certainly historians should be able to deduce this as another of Hitler's delusions.

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Sources and Further Reading

• Dirks, Carl: Der Krieg der Generäle. (1999)

• Lunde, Henrik O.: Hitler’s preemptive war: The Battle for Norway, 1940. (2009)

• Manstein, Erich v.: Verlorene Siege. (1955)

• Mazower, Mark: Hitler's empire: how the Nazis ruled Europe. (2009)

• Piekalkiewicz, Janusz: Der Wüstenkrieg in Afrika. 1940-1943. (1985)

• Piekalkiewicz, Janusz: Der Zweite Weltkrieg. (1985)

• Schendemann, Heinrich: Die wirtschaftliche Zusammenarbeit zwischen dem Deutschen Reich und der Sowjetunion von 1938 bis 1941. (1993)

• Wucher, Albert: Seit 5 Uhr 45 wird zurückgeschossen - Ein Dokumentarbericht über Vorgeschichte und Beginn des Zweiten Weltkrieges. (1959)

• Zentner, Christian: Der Zweite Weltkrieg. (1981)