Short answers, pulled from the story.
The title most likely refers to Nicomachus, either Aristotle's son or his father, both of whom bore that name. One theory is that the work was dedicated to his son; another is that the son edited it, though he is believed to have died young. A third possibility is that it was dedicated to Aristotle's father. Scholars agree it was probably not prepared by Aristotle himself for publication, but rather resembles lecture notes.
Eudaimonia is a Greek word Aristotle used for the highest good for human beings. It is often translated as flourishing or happiness, but it refers to an active way of living in accordance with reason and virtue across a full lifetime, not a passive emotional state. Aristotle argued it must be measured over a whole life, not judged by any single moment.
Aristotle proposed that each virtue sits at a mean between two corresponding vices, one of excess and one of deficiency. Courage, for example, lies between cowardice and rashness. He acknowledged this idea predated him; the Delphic motto 'nothing in excess' was much older than Socrates. He also noted that people tend to drift toward the more pleasurable vice, so it helps to steer deliberately toward the less pleasant extreme when seeking the mean.
After Aristotle's death, his library passed to Theophrastus and then to Neleus of Scepsis, whose heirs hid the collection in a cellar to prevent seizure by the Kingdom of Pergamon. The texts stayed there for roughly a century and a half in poor preservation conditions. A collector named Apellicon purchased the library, returned it to Athens, and had the degraded texts recopied with guesswork filling the gaps. When Sulla seized Athens, he took the library to Rome, where Andronicus of Rhodes organized it into the first complete edition of Aristotle's works.
Albertus Magnus introduced the synthesis of Aristotelian ethics with Christian theology, and Thomas Aquinas produced the most important version of that synthesis. Aristotle became known simply as 'the Philosopher' in Aquinas's writings. Protestant universities still treated the Nicomachean Ethics as the main authority on ethics well into the seventeenth century, with over fifty Protestant commentaries published before 1682.
Aristotle distinguishes two main senses of justice: being law-abiding and being equitable or fair. He divides particular justice into distributive justice, which allocates shared goods in a ratio that respects the relative standing of the parties, and restorative justice, which remedies harm in transactions. He rejects the Pythagorean idea that simple retaliation constitutes justice, arguing it ignores the reasons behind an act and fails to respect the prior status of the parties.