Short answers, pulled from the story.
Tin Pan Alley was located on West 28th Street between Fifth and Sixth Avenues in the Flower District of Manhattan. On the 2nd of April, 2022, the City of New York officially co-named that stretch of 28th Street "Tin Pan Alley."
Tin Pan Alley is generally dated from around 1885, when music publishers began concentrating in the same Manhattan district. Its end is disputed; some historians date it to the Great Depression in the 1930s, while others place it in the 1950s when rock and roll displaced earlier styles.
Monroe H. Rosenfeld is most often credited with coining the term in the New York Herald, with the Grove Dictionary of American Music dating its first use to 1903. A competing account credits a journalist interviewing songwriter Harry von Tilzer, whose modified piano reportedly sounded like a tin can. The name was firmly in use by the fall of 1905.
Song pluggers were pianists and singers hired by music publishers to demonstrate and promote sheet music sales. George Gershwin, Harry Warren, Vincent Youmans, and Al Sherman all worked as pluggers early in their careers. A more aggressive form called "booming" involved buying tickets to public events and singing a target song repeatedly until crowds absorbed it.
Tin Pan Alley attracted Irving Berlin, George Gershwin, Scott Joplin, Fats Waller, Harold Arlen, Dorothy Fields, Cole Porter, Hoagy Carmichael, and George M. Cohan, among many others. The full list of composers and lyricists connected to the Alley spans several generations of American popular music.
ASCAP, the American Society of Composers, Authors, and Publishers, was founded in 1914 to protect the financial interests of established publishers and composers connected to Tin Pan Alley. New members were only admitted with sponsorship from existing members.