Don’t bother: it will only confuse the issue. He never wrote a book on the concept, having changed directions well before his collapse. The book of that title was cobbled together from leftover scraps: some he rejected, some he re-wrote and used elsewhere, some that were only thought-experiments, and some that were actually quotes from books he was reading! The structure given to those scraps was based on someone else’s (inaccurate) understanding of what he meant.
Not at all; most of his work was published long before she took change of his literary estate. There were a few pieces cut from Ecce Homo’s early printings, and one of them is absent from the Kaufmann translation because it had not yet been recovered, but it has since been restored to the original German. She also oversaw publication of Antichrist, but I can’t recall anything being excised from it; if so, it has long since been restored to his draft version.
I wish I had more time to write this morning, as this is something I’ve spent a long time on. But I’ll try to answer as quickly as I can, and at least give you a few bits to think about.
I think it is wrong to approach will to power as a metaphysic (like Heidegger) and it is dead wrong to think of it as a telos, but I think he did mean it in a very real, literal sense. Nietzsche had studied a lot of contemporary natural sciences, from the physics of Boscovich and Mach to the Naturphilosophie of Goethe and Schelling to the biology of Roux and Nägeli. He was particularly taken with biology, and engages in his writings with a version of Darwinism (drawn second-hand from Rée, Lange, Nägeli, Rolph, Roux, Strauss, and others), with the teleological development of Kant and his followers, and the theorists of a vital force (Bildungstrieb or Lebenskraft) like Blumenbach et al.
From this extensive engagement, in publications, notebooks, and annotations in the books he owned, one can draw certain conclusions about how we saw will to power active in the world. For him it was a replacement for theories of Bildungstrieb, but (ostensibly) free of the taint of telos and metaphysics of such others. It was not so much a vital force as a simple description of what life is: dynamism and change. As Nietzsche observed, the tiniest forms of life (microbes, etc.) do not consider their options: they do not think about ‘preserving’ themselves in a ‘struggle for existence’, or consider their hunger for sustenance–they simply act, overpowering what they can to feed and reproduce. What is it that drives them forward? More broadly, what is it at root that drives all lifeforms forward: to act, change, be? Nietzsche’s answer is will to power.
It is important to distinguish this from willing as such, and from Schopenhauer’s will to life. Nietzsche actually came to the opinion that there was no such thing as the will (just as he argued that there was no such thing as the ego, or the individual). Willing was not a conscious activity for him, and will to power is not something that you have or use. It really is a description of natural processes, and outside dealings with fundamental properties of life itself, it is not much use as an explanatory tool for philosophy. It is also part of a lengthy engagement with–and utter rejection of–Schopenhauer’s will to life, which was at times folded back into his misreading of Darwin’s theory as a reactionary will to life. Such a will would impute conscious motive and purpose to life, and both of these were anathema to Nietzsche. Schopenhauer saw in all lifeforms a clear end-directedness related to the preservation of life; for Nietzsche this is a clear error, since it implies forethought, and his suggested replacement as a fundamental motive is the desire to change, overpower, overcome, consume, dominate–i.e., will to power.
This is quite impossible to summarize quickly, but if the topic is interesting I can pull quotes and pieces in and we can talk about details of how he saw will to power functioning, and about what he hoped it would accomplish for philosophy, and even from the sources he drew upon to defend the idea. My dissertation is on Nietzsche’s relation to science, so I’ve tonnes of material floating ‘round the house. I do hope this was a good start, tho’, and that it was in some way helpful.