Short answers, pulled from the story.
Xbox Live Arcade launched on the 6th of November 2004 for the original Xbox. The service was officially announced at Microsoft's E3 press conference on the 12th of May 2004. Access required ordering a disc from Microsoft's website, which also included a free copy of Ms. Pac-Man.
As of October 2016, 709 titles had been released on Xbox Live Arcade for the Xbox 360, with an additional 27 titles released for the original Xbox.
The original size limit was 50 MB, set to fit within a 64 MB Xbox memory unit. Microsoft raised the cap over time to 150 MB, then 350 MB, then 2 GB. On the 12th of September 2012, two titles exceeded even that ceiling: Red Johnson's Chronicles at 2.68 GB and Double Dragon Neon at 2.24 GB.
The Summer of Arcade was a Microsoft promotion that debuted on the 30th of July 2008. In 2008, downloading eligible titles, including Braid and Castle Crashers, entered players in a prize draw for 100,000 Microsoft Points and an Xbox 360 Elite console. Later editions in 2009 and 2010 offered point rewards for purchasing a full lineup of games.
Most removals were caused by publisher licensing disputes, not Microsoft's formal delisting policy. Nine Midway Games titles were removed in February 2010 following Warner Bros.'s acquisition of Midway assets. Teenage Mutant Ninja Turtles: Turtles in Time Re-Shelled was removed on the 30th of June 2011 when its license expired, and Marvel vs. Capcom 2 was removed in late December 2013 at Capcom's announcement.
The average conversion rate across all Xbox Live Arcade titles was 18 percent, meaning roughly 18 out of every 100 trial downloaders went on to buy the full game. The range ran from a low of 4 percent to a high of 51 percent depending on the title.