Short answers, pulled from the story.
Ignaz von Seyfried served as musical director from 1797 until 1826. This tenure spanned nearly three decades of constant activity within the new building known as the Theater an der Wien.
Wolfgang Amade Mozart and Johann Georg Albrechtsberger instructed Ignaz von Seyfried directly. These lessons occurred before 1791 when Mozart died, and Seyfried later edited Albrechtsberger's complete written works after his teacher passed away.
Ignaz von Seyfried wrote accounts of Mozart death a few weeks after The Magic Flute premiered. His handwritten memoirs contain these stories which David J. Buch analyzed in Eighteenth-Century Music volume two.
Ignaz von Seyfried conducted the premiere of Beethoven original version of Fidelio in 1805. He also worked with Ludwig van Beethoven on Piano Concerto No. 3 and the Choral Fantasy during this period.
Ten masses were among Ignaz von Seyfried output including one written for double choir. His catalog also included motets, requiems, psalms, hymns, oratorios, two symphonies, cantatas, chamber music pieces, concertantes for clarinet and oboe plus ten serenades for four waldhorns.