Short answers, pulled from the story.
Pope Martin V arrived on the 28th of September 1420 after a journey that began in May. He found the city stripped of population and security during decades of absence by previous popes who had fled to Avignon.
Sandro Botticelli, Pietro Perugino, Pinturicchio, Domenico Ghirlandaio, and Cosimo Roselli created frescoes depicting Life of Moses and Life of Christ. Fresco work began in 1481 and concluded in 1482 with marble screen and choir stalls completed that same year.
Bramante laid the cornerstone of the new Basilica of St Peter on the 18th of April 1506 while uniting Vatican Palace with Villa Belvedere. The project involved expanding the body with five aisles and longitudinal cross vaults on pillars incorporating old columns.
The brutal Sack of Rome in 1527 by troops of Emperor Charles V brought Roman High Renaissance to abrupt end. Some artists were killed while most fled to other cities along with patrons from Curia before activity revived mostly in Mannerist style.