I'll stick to this thread as you suggested.
The problem is when Schop talks about Will objectifying itself, as Will does not do "causality-like" things. — schopenhauer1
He does say that willing is causality seen from the inside, so to speak, though this is to speak metaphorically. As you know and have said, the only legitimate application of this concept is in relation to the world as representation, wherein physical bodies interact with one another in space and time. However, one of these bodies
is my own. With all other objects, I know them superficially, but my own body I inhabit and know interiorly, which is to say, I know it as it is in itself, not merely as it appears. What is my body subjectively in itself? Not an object but a will, which then provides the key to understanding what all other objects are in themselves. The will, moreover, only wills one thing as a timeless act of will: life. The knowledge of distinct, individual objects and acts of will is, therefore, ultimately illusory.
In willing life, so too does the will simultaneously will knowledge of itself, the miracle par excellence as Schopenhauer calls it. Why is it a miracle? Because there is no
reason the will should become aware of itself since the will has no reason for its existence to begin with. When you said that the PSR only applies to representations, not to the will itself, you were absolutely correct, but the will can still be and is the logical ground of representation. So we can ask: what grounds representation? The answer is the will. If we then ask what grounds the will, the answer is nothing. The will is groundless.
Being the reason or ground for something is not to be its cause. Reasons and causes are different things. Hence, the will did not and does not paradoxically cause representations to exist at some primordial point in time when a particular organism came on the scene and became self-conscious. It is rather the ground for the world as representation's existence. This is why what Schopenhauer is doing is called metaphysics and not physics. He's seeking a rational, philosophical explanation for the existence of the world, not a causal or physical one. This isn't to say the latter are not legitimate modes of explanation, however. The story we can tell about the evolution of inanimate matter, to simple celled organisms, and then to more complex forms of life is a perfectly legitimate explanation for our existence, but it's not the only one and is one-sided. So from this empirical perspective, it is true to say that the "first open eyed" organism is necessary in order to account for the world as representation, but only from this limited perspective.