The Soviets were no less war wearythan anyone else. They lost 20 million people.1. Actually, yes, the start date would have had to be immediate...because the longer we had waited, the greater the repairs and improvements that the Soviets would have made to their lines of communication.
2. The quality, the discipline and training of the German soldier was the best in the world...and look what the Soviets did to them. You're stuck on the assumption that we were, are, and always will be the best at everything...and you're greatly underestimating your opponent.
3. Yes, there were commissars...but you're also assuming that patriotism was somehow foreign to the Soviet soldier. In THEIR eyes, the commissar was for the cowards who ran away. And they would have fought every bit as hard against us as against the Germans. Why? The regular soldier didn't know much about the Germans except that they'd invaded once already...and it would have been simplicity itself to point out to the Soviet soldier that the British and Americans had already invaded Russia before to prevent the success of communism.
4. The B-29's wouldn't have been available until after the surrender of Japan...and after not only the B-29's were transferred, but also all their specialized support equipment. And let's not forget that they needed longer-than-normal runways to use, too. And on top of all that, you're assuming that by September - five months after the commencement of hostilities with the USSR (with their much greater forces and their much shorter supply lines) - that we'd still be holding France.
AND let's not forget that the world was war-weary. It is unlikely in the extreme that the American and British public would have supported a continuation of the war against the USSR...because that's one of the big differences between totalitarianism and democracy. A democracy is more productive per person than a totalitarian state...but a totalitarian state doesn't have to bow to public pressure. Or did you learn nothing from Vietnam?