Short answers, pulled from the story.
The classical period in music spanned from approximately 1730 to 1820. This era began around 1750 when Johann Sebastian Bach died and ended with the deaths of Beethoven and Schubert in the late 1820s.
Joseph Haydn, Wolfgang Amadeus Mozart, and Ludwig van Beethoven formed the First Viennese School during the classical period. Other significant figures included Christoph Willibald Gluck, Carl Philipp Emanuel Bach, Domenico Scarlatti, Franz Schubert, and Ludwig van Beethoven.
Classical music emphasized homophony where a clear melody line sits over subordinate chordal accompaniment. Composers used sonata form and structures like the symphony and string quartet while moving away from dense Baroque polyphony.
The fortepiano replaced the harpsichord as the main keyboard instrument by the early 1800s due to its ability to play louder or softer. Orchestras increased in size and standardized sections including woodwinds, strings, brass, and percussion.
The classical style ended after 1790 when composers like Schubert and Hummel pushed toward Proto-Romantic styles. The decline was precipitated by the deaths of Beethoven and Schubert marking the final eclipse of the Classical style in Vienna.