Short answers, pulled from the story.
Groundbreaking on the third Madison Square Garden took place on the 9th of January 1925. Thomas W. Lamb designed the theater as a simple box compared to the ornate towers of Stanford White's second Garden.
Boxing promoter Tex Rickard assembled backers he called his 600 millionaires to fund the project. The arena was built at the cost of $4.75 million in just 349 days.
On the 17th of January 1941, 23,190 people witnessed Fritzie Zivic's successful welterweight title defense against Henry Armstrong. This crowd size remains the largest recorded at any of the Gardens.
The New York Americans began play in 1925 and officially opened the Garden by losing to the Montreal Canadiens 3-1. Both teams played at the venue until the Americans suspended operations in 1942 due to World War II.
Penn Station's owners Pennsylvania Railroad announced they sold their air rights to the Madison Square Garden Corporation on the 3rd of November 1960. Demolition of Penn Station commenced in 1963 with major controversy surrounding the destruction of a historic architectural landmark.