As regards your first question, the very brief answer, which we have from his writings in Mein Kampf and the unnamed and unpublished "Second Book", is that he wanted to conquer a vast amount of land to the east as Lebensraum to set Germany up as one of the two superpowers in a bi-polar world, the other being the United States, which Germany would then be able to compete directly with both economically and potentially militarily, although this was not an explicit requirement. At least initially, Hitler hoped that the United Kingdom would ally itself with Germany in a partnership against the US, but obviously this never came to pass. So the sum of it is that Hitler absolutely desired to place Germany on a path to triumph as the lone-super power in a unipolar world. That didn't necessarily require literal world conquest by military might, but it certainly was based on a vision of economic superiority. This is expanded on to some degree in this previous answer I wrote here.

As regards your second question, hopefully someone else can come along and provide you with a more in-depth analysis of Nazi racial pseudoscience.