You indicate that you’re “not entirely clear on” a couple of assertions of Nisargadatta. 

 “The world is something in consciousness,” is evident when we consider that when our animated consciousness is absent (as in death; under anesthesia; indeed, even in deep sleep), the world itself is not a perceived reality. Thus, what we know as the world appears only within the framework of our animated consciousness. More yet, in the condition of death, etc., even the very idea that there is such a state as “consciousness” disappears. What we are is nothing more than one of the manifold appearances of the eternal.

Nisargadatta goes on to compare the eternal state to that of an “unborn child”—no consciousness of a world, or even of a consciousness itself.

And in our eternal state, there is not even such a reality as “one.” So, this pertains to your pondering, “is everything actually one?”

Therefore, Nisargadatta can say not even a “one,” as opposed to a “not-one”.

[From audio recording #193.]