Short answers, pulled from the story.
The Ed Sullivan Theater opened its doors on the 30th of November 1927, as Hammerstein's Theatre. Architect Herbert J. Krapp designed the building to resemble a cathedral rather than a traditional Broadway theater.
Arthur Hammerstein operated the venue from 1927 until he lost it to foreclosure in February 1931. He filed for bankruptcy claiming he had only $5.77 remaining after losing two million dollars in preceding years.
CBS officially renamed the theater after Ed Sullivan on the 10th of December 1967. The network paid $100,000 annually for the lease which expired in 1976.
Seat count dropped to four hundred during the renovation for David Letterman's new show. Audience capacity reduced from 461 seats down to 370 with larger chairs installed.
Stephen Colbert succeeded David Letterman as host beginning the 8th of September 2015. The Letterman set was removed one week after his final show on the 20th of May 2015.