Time was heavily against Germany when it came to challenging the Soviet Union, who was still recovering from the Red Army purges by the time of the invasion but was increasing production of military equipment on all fields as the Red Army reformed.

Due to the holes in the Red Army's chain of command brought on by the purges, the structure of the Red Army was mired in communication problems that was apparent to everyone during the Winter War, where the Soviets were bogged down fighting Finland and only muscled their way to victory against them at a heavy cost in men. Hitler and the OKW viewed this as a sign of Red Army weakness, and an opportunity to strike at the Soviet Union while they were still weak.

but between 1939 and 1941, Soviet military production increased dramatically, where between the 2 years, Red Army divisions increased from 131 to 316 divisions, artillery and mortar pieces increased from 55,800 to 117,600, and military aircraft increased from 7,700 to 18,700. This Soviet buildup in the last two years, along with promotions of new officers to fill the holes in the chain of command meant that the Soviet Union could defeat Germany in a conventional war if something was not done quickly, so Barbarossa was approved in December of 1940 in order for an invasion to be ready before the Red Army finished its buildup and reforms. (source)

This rapid buildup also led to the Germans having downright awful intelligence on the state of the Red Army prior to Operation Barbarossa, only having acquired outdated intelligence from 1939 that led the OKW to assume that the Soviets were only able to field 100 frontline divisions and call up to 50 in reserve, when the truth was that the Soviet Union could call more than 300 divisions to the front by November 1941. This was on top of very limited intelligence on Soviet artillery and tanks, with the introduction of the T-34 and KV-1 to the battlefield being an almost complete surprise to the Wehrmacht, with the Heer having to call in science teams to assess the Soviet tanks in order to draw designs for new counters to Soviet armor such as the Tiger I and Panther tanks.

In short, When Britain refused to surrender quickly, Hitler could not just wait to attack the Soviet Union later. The Red Army was not standing idly by with holes in their chain of command for very long, they were in the middle of a massive military overhaul that would've outmatched the Germans if it continued to build to its full strength. Hitler sought to strike while the red army was still disorganized, but Barbarossa was a rushed plan that was honestly extremely overoptimistic and severely underestimated the Soviets ability to produce weapons and replace lost manpower, ultimately failing.

Sources:

Glantz, David (2012). Operation Barbarossa: Hitler's invasion of Russia 1941. The History Press.

Glantz, David (2010a). Barbarossa Derailed: The Battle for Smolensk, Volumes 1 and 2. Helion & Company.

One last thing was just as you said, Hitler demanded resources to prosecute the war and achieve national self-sufficiency, which dictated the first few years of the war as a German scramble for resources. Farmland and food for the Wehrmacht from France and Poland, Iron and Aluminium in Norway/Denmark, and oil from Romania.

But even with Romania's oil fields fueling Germany, the Wehrmacht was still consuming around 25% more oil than could be produced within Germany's controlled territories. To get around this, the Molotov-Ribbentrop pact contained other provisions that followed up aside from just the partition of Poland. In it was also a large trade agreement where the Soviet Union would supply 500,000 tons wheat, cotton, and most importantly, 900,000 tons of oil to Germany in exchange for locomotives, diesel engines, turbines, and machine parts from Germany.

This trade agreement, however, gave Stalin economic leverage over Hitler which he despised. The fear that the Soviets could simply embargo oil shipments to Germany and cripple the war effort convinced Hitler that he needed the seize the oil fields for himself in order to achieve economic autarky, adding another degree of agency to the timing of the attack.

Sources:

Rich, Norman (1973). Hitler's War Aims Ideology: The Nazi State and the Course of Expansion. W.W. Norton

p. 367-369 Schwendemann H. Die wirtschaftliche Zusamenarbeit zwischen dem Deutschen Reich und der Sowjetunion von 1938 bis 1941. Berlin, 1993