Good post. However, I would like to make a correction. During WWII, Winston Churchill (later joined by FDR) imposed a food blockade on Germany. The Hunger Plan was the Nazi government’s effort to deal with the resulting food crisis. The Hunger Plan involved the starvation of captured Soviet cities; so that the food which would otherwise have fed those cities could instead be used to prevent starvation elsewhere in the Reich.
The plan had never been to starve Soviet POWs. Those POWs were conscripted to work in German weapons factories. Everyone, from Hitler on down, recognized those POWs were an essential component of Germany’s war machine. That is why Hitler ordered the POWs to be fed.
However, the Reich lacked the manpower necessary to cordon off captured Soviet cities from the Soviet countryside. Due to the lack of that manpower, the Nazis were unable to prevent food from flowing from the captured Soviet countryside to captured Soviet cities. The Hunger Plan mostly failed: the planned starvation in captured Soviet cities mostly did not occur. That failure didn’t result in fewer deaths. Just different deaths than those the Nazi government had envisioned with their Hunger Plan. Due to the failure of the Hunger Plan, the man tasked with feeding the Soviet POWs didn’t have the food he needed to carry out the order Hitler had given to him: the order to feed the Soviet POWs. Because it was physically impossible for that man to carry out his orders, millions of Soviet POWs starved to death while in German captivity.
The Nazi leadership had deep-seated fears about Germany’s food situation. One of the reasons Hitler wanted lebensraum was so that Germany could physically feed itself, even if Britain imposed a food blockade. (As it did in WWI, and as Churchill again did in WWII.) The two most vital resources Hitler required from the western Soviet Union were food and petroleum. For Barbarossa to have been successful from the Nazi perspective, Germany needed to capture a considerable portion of Soviet oilfields, and a considerable portion of Soviet farmland.
To address your question of what Hitler should have done differently: he should have placed von Manstein in charge of Barbarossa in its entirety. Doing so would have resulted in a far greater level of success. Moscow and Leningrad almost certainly would have fallen in 1941, paving the way for additional German successes in 1942.