From sea to shining sea and leave empires like the British, Japanese, German, Russian to fight for global domination, huh?

That's a very different worldview from FDR too.

It's not a good plan because the empire that finally achieves hegemony over the rest of the world would eventually come for the USA in due course and then you'd be on our own.
As to the third point, there's a lot of ifs both ways. As I said, we've very different worldviews.

Regards

Mike