For one thing, I never used the word conquer. I said "wanted" and "dominate". Second of all, do you really thing Adolf Hitler would pass up the opportunity to take it, if it presented itself? The man always went beyond his stated desires at nearly every stage, so I don't think Hitler's own self stated limits hold much weight considering, it is you know HITLER we are discussing.
That gets into whole another realm of Hitler's attachment to reality. I merely stated he wanted the world, and once again nothing in his history indicates that his own material limits ever presented an obstacle in his mind. Otherwise he never would have attacked the Soviet Union and/or the US.
Hitler can want whatever he wants, that doesn't mean he's gonna get it. Germany simply can not dominate the globe in his life time and after the Soviets are defeated Hitler will have no problem standing down and developing his pan-European Empire (assuming he is at peace with Britain and the USA). Remember that Hitler wanted a pan-European superstate capable of competing
with America. He wasn't silly enough to think he could defeat America within his lifetime.
A question of timing. It was very possible to defeat Britain in 1940. And like William Pitt the Younger noted regarding a Napoleon dominated a Europe, a pan European superpower would eventually come to possess the means by which to defeat the British if left unchecked.
Britain can be brought to make peace
in 1940, or later if the USSR is defeated and the USA isn't in the European war. But invaded and conquered or puppetized? No way.
The idea is that the USA will be in a military alliance with the UK thus nixing the economic overpowerment argument. Keep in mind that in this scenario the US and Britain will be in an alliance technically only against Japan but after the UK makes peace with Germany this will rapidly evolve into a general alliance.
In a World War II timeframe yes, but a trans-European Empire with access to Caucasian and Middle Eastern oil, would possess the means not long afterwards and certainly before the 1980's to do so.
Even then I highly doubt this empire would have the logistical capability to directly invade and conquer the mainland USA. Also even if Germany does get nukes the USA will be way ahead of them both in quality and numbers. Germany will be at an atomic deficit similar to the way the USSR was in the 1950's.
The problem with your contention is that it is predicated on Hitler being 1) realistic and 2) credible when he says "this and no more" and Hitler was famous for being neither. On the other hand he was known for was megalomania and delusions about his own abilities and that of his Third Reich.
Hitler may have been insane but he was not stupid. I don't see why he would start another war when all of his war aims have been reached and he is free to develop his New Order in Europe. Especially seeing as by this time it will be clear that Japan is on the way out and he will have to face the USA/UK all by himself.