Short answers, pulled from the story.
The Venetian School began in 1527 following the Sack of Rome which displaced musicians from the papal court. Venice emerged as a safe haven where creative energy could flourish without fear of invasion.
Adrian Willaert became maestro di cappella at St Mark's Basilica in 1527 and remained there until his death in 1562. He developed a grand antiphonal style that used groups of singers and instruments playing sometimes in opposition and sometimes together.
St Mark's Basilica featured opposing choir lofts separated by wide arches and high vaults that created noticeable sound delays for listeners seated on the floor below. Architects designed the building to create an acoustic environment where silence was not empty but filled with echoes allowing composers to exploit natural sound delays.
A progressive faction led by Baldassare Donato clashed repeatedly with a conservative group headed by Gioseffo Zarlino. Friction between them reached its peak in 1569 during a dramatic public conflict at the Feast of Saint Mark.
The year 1580 marked the beginning of an extraordinary period when Andrea and Giovanni Gabrieli composed enormous works for multiple choirs. Their compositions represented the first known instances where specific dynamic markings appeared in printed music along with detailed instructions for ensemble instrumentation.