Short answers, pulled from the story.
The Roman Empire began in 27 BC when the Senate granted Octavian the title of Augustus and recognised him as the first Roman emperor. The Western Roman Empire ended in 476 AD when Romulus Augustulus was deposed by Odoacer, while the Eastern Roman Empire survived until the fall of Constantinople in 1453.
The Roman Empire reached its largest extent under Trajan, encompassing around 5 million square kilometres. Its population of 55-60 million inhabitants, by traditional estimates, accounted for between one-sixth and one-fourth of the world's total population.
The Five Good Emperors were Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius, all members of the Nerva-Antonine dynasty. Hadrian is particularly noted for consolidating the empire's frontiers and for refounding Jerusalem as the Roman colony Aelia Capitolina around 129-130 AD.
The Western Roman Empire fell due to a combination of civil wars, barbarian invasions, economic disorder, and the assimilation of Germanic peoples of dubious loyalty to Rome. The conventional end date is 476 AD, when the Germanic warlord Odoacer deposed the emperor Romulus Augustulus.
Slavery was central to the Roman economy. At the time of Augustus, as many as 35% of people in Roman Italy were enslaved. Outside Italy the enslaved population averaged an estimated 10 to 20% of residents. Unlike Greek city-states, Rome allowed freed slaves to become citizens, with full rights extending to their future children.
Latin and Greek were the primary languages of the empire, though the empire was deliberately multilingual and supported many local tongues including Coptic, Aramaic, Punic, Gaulish, and others. After the western empire collapsed, spoken Latin fragmented into the incipient Romance languages by the 7th century AD.