Short answers, pulled from the story.
Mozart's Sinfonia Concertante for Violin, Viola and Orchestra in E major, K. 364 (also catalogued as K. 320d), was composed in 1779. Mozart wrote it while traveling through Mannheim and Paris. Scholar Simon P. Keefe has described it as "a concerto in all but name."
The solo viola part is written in D major while the rest of the orchestra plays in E major. Mozart instructed the violist to tune the instrument a semitone sharper using scordatura technique, which produces a more brilliant tone and helps the instrument project over the orchestra.
Richard Wigmore, writing in Gramophone in October 2015, rated a recording by Iona Brown and Lars Anders Tomter with the Norwegian Chamber Orchestra on Chandos CHAN9695 as the best to date. A 1989 recording with Iona Brown and Nobuko Imai also made his short list, alongside a notable 1951 Casals Perpignan Festival recording with Isaac Stern and William Primrose.
In 1808 an uncredited arrangement of K. 364 was published under the title Grande Sestetto Concertante, scored for string sextet. Unlike the original, all six parts are distributed equally among the six players rather than presenting soloists with accompaniment.
Composer Michael Nyman used variations on the slow second movement for the soundtrack to Peter Greenaway's 1988 film Drowning by Numbers. The original piece is also heard in the film after each of the drownings in the screenplay.
George Balanchine created a choreographic realization of K. 364 danced by students from the School of American Ballet, which premiered at Carnegie Hall in 1945. The professional premiere was given by Ballet Society at New York City Center. The ballet is no longer in the current New York City Ballet repertoire; American Ballet Theatre has most recently performed it in New York City.