I appreciate the assessment, but I don't think your definition of "nature" as "whatever exists" helps much in a debate about naturalism, since naturalism's supposed to be distinguished from supernaturalism. If God exists, then God would be natural, by your definition. So that definition begs the question.

Look more carefully: my reference to what nature is "at bottom" didn't come out of nowhere; rather, it's another way of saying what nature is "fundamentally" or in its foundations. The sciences are likewise divided in that way. Biology describes a high level of emergent properties, whereas physics is supposed to be more fundamental because it's more universally applicable.

My instrumental definition of "nature" as "whatever's subject to scientific objectification and industrial exploitation" helps distinguish nature from supernature without begging the question. That's its purpose.

So I never said that nature in its entirety is mindless since that would contradict my property dualism and humanism. Nature includes us and we obviously have minds. No, what I said is that nature is fundamentally mindless, meaning that physicists don't deal with mental properties and thus physics is functionally atheistic. That is, atheism is consistent with a naturalistic description of ultimate, deepest, most universal, scientifically objectified reality.

The higher levels of nature are real, too, but they're dependent on the lower levels so there's an asymmetry there. But this is indeed a mystery. Some physicists, too, are inclined to treat the higher-level things as epiphenomena, illusions, or holographic projections of the lower, atomic level. This sort of model helps make sense of the asymmetry that's built into the fruits of scientific analysis and objectification. So somehow philosophical naturalists need to make sense of it too.