Short answers, pulled from the story.
Kakifly wrote and illustrated the K-On! manga series, which was serialized in Houbunsha's Manga Time Kirara magazine between the 5th of May 2007 and the 10th of October 2010. The series relaunched from the 8th of April 2011 to the 9th of June 2012 with two separate storylines published in Manga Time Kirara and Manga Time Kirara Carat.
Yui Hirasawa plays the guitar and eventually masters a Heritage Cherry Sunburst Gibson Les Paul Standard. She began her musical journey playing castanets before ever touching a guitar and initially had no experience reading sheet music or playing any instrument.
Sawako Yamanaka was formerly the lead guitarist and vocalist of a heavy metal band called Death Devil, performing under the stage name Sawako. She served as the club's adviser and was able to substitute for Yui at the school festival with almost no notice.
The real-life rural town of Toyosato, Shiga, became a pilgrimage site for fans after the elementary school in Toyosato served as the model for the high school in the anime. The Kyoto prefectural government used K-On! to promote the census and encourage people to be counted in 2010.
The second season's opening theme Go! Go! Maniac became the first anime image song to ever top the singles chart. The band also became the first female vocalists to occupy the top two spots on the singles chart in 26 years since Seiko Matsuda in 1983.
The anime film was released on the 3rd of December 2011 and earned a total of ¥1,639,685,078 (US$21,419,792) by the end of its run. Fans visited the London cafe inspired by the Troubadour Cafe in Earl's Court after the film's release.