Short answers, pulled from the story.
Chiang Kai-shek appointed Tang Shengzhi to command the hastily assembled Nanjing Garrison Force on November 25. The defending army numbered between 73,000 and 81,500 men according to most reliable estimates.
By December 2, the Shanghai Expeditionary Army captured Danyang more than five days ahead of schedule. This rapid movement left supply lines far behind forcing Japanese soldiers to loot civilians along the route.
On December 12, Japanese naval aircraft led by Lieutenant Shigeharu Murata attacked and bombed the vessel which sank at 3:54 pm. Two crewmen and one civilian died while another forty-three crew members and five civilians were wounded.
He believed holding Nanjing would prove China's resolve to Western powers attending the Nine Power Treaty Conference. Chiang also hoped it would strengthen his position for peace talks mediated by German ambassador Oskar Trautmann.
Over the course of the battle roughly 1,000 Chinese soldiers were shot dead by members of their own army for attempting retreat. This occurred as units disintegrated in open retreat after Tang Shengzhi escaped across the Yangtze River on December 13.