Short answers, pulled from the story.
The modern English term Easter derives from an Old English word that usually appears in the form Eostre, Ostara, or Estera. In the 8th century AD, Anglo-Saxon monk and scholar Bede recorded in his The Reckoning of Time that this name referred to a month corresponding to April.
Direct evidence for a fully formed Christian festival of Pascha begins to appear in the mid-2nd century. Perhaps the earliest extant primary source referring to Easter is a mid-2nd-century Paschal homily attributed to Melito of Sardis.
The settlement of the controversy about the Paschal season caused by the Quartodeciman practice is listed as one of two reasons emperor Constantine convened the First Council of Nicaea in 325 AD. Letters from individuals present at the council mention a decision prohibiting Quartodecimanism and requiring all Christians adopt a common method to independently determine Paschal observance.
Easter is the third Sunday in the paschal lunar month or the Sunday after the 14th day of that lunar month. Since the ecclesiastical new moon falls between March 8 and April 5 inclusive, the paschal full moon must fall between March 22 and April 18 inclusive.
The egg is an ancient symbol of new life and rebirth that became associated with Jesus's crucifixion and resurrection in Christianity. The custom originated in the early Christian community of Mesopotamia who stained eggs red in memory of Christ's blood shed at his crucifixion.