Short answers, pulled from the story.
Andronicus of Rhodes compiled Aristotle's Metaphysics in the first century BC. The work consists of lecture notes, drafts, and fragments arranged by later editors rather than being a polished treatise written by Aristotle himself.
The title Metaphysics means after the physics and reflects the historical order of Aristotle's works in the library. Aristotle never called it Metaphysics and instead referred to the subject as First Philosophy or the study of being qua being.
The unmoved mover is the most divine entity described as the thinking of thinking and pure actuality with no potentiality. This entity serves as the final cause and goal toward which all things strive without creating the universe in a temporal sense.
The transmission of the Metaphysics to the medieval world was facilitated by Arabic Aristotelian scholarship peaking with Ibn Rushd known as Averroes. William of Moerbeke translated the text into Latin using Greek manuscripts that are now lost and this enabled commentaries by Albert the Great and Thomas Aquinas.
W. D. Ross produced a critical edition of the Metaphysics in 1924 and Werner Jaeger produced another in 1957. New critical editions of books Gamma, Alpha, and Lambda have been produced since 1970 with different versions of the stemma codicum proposed.