Short answers, pulled from the story.
Wolfgang Amadeus Mozart wrote Symphony No. 1 during the summer of 1764 while living at 180 Ebury Street in Chelsea. The eight-year-old composer created the piece after his family relocated to London for a Grand Tour of Europe.
The handwritten original score survives today at the Biblioteka Jagiellońska library in Kraków. This institution holds the physical document written by Mozart himself during his childhood years.
Johann Christian Bach served as a major influence on the young composer during his stay in London. Leopold Mozart also shaped the structural composition through his guidance and teaching methods alongside contributions from the sons of Johann Sebastian Bach.
The orchestra requires two oboes, two horns tuned in E, and string instruments for the full score. Horns state the four-note theme prominently within the orchestral texture throughout the three distinct movements.
Public audiences heard the work for the first time on the 21st of February 1765. The premiere occurred shortly after the family settled into their temporary home in Chelsea following their move from Ebury Street.