Short answers, pulled from the story.
Abel Seyler was born on the 23rd of August 1730 in Liestal, a small town outside Basel. He grew up in a family that valued piety and learning before moving to London and later settling in Hamburg during the 1750s.
The collapse of Abel Seyler's banking firm resulted from the Amsterdam banking crisis of 1763 which led to debts ranging between three and four million Mark Banco. The companies engaged in complex speculation with financial instruments and leased a mint factory in Rethwisch in 1761 to produce debased coins for the Duke of Schleswig-Holstein-Sonderburg-Plön.
Following his financial collapse, Abel Seyler devoted himself entirely to theatre starting in 1767 when he used his remaining funds to become the main shareholder and effective leader of the idealistic Hamburg National Theatre. This institution aimed to establish a national theatre based on ideas from Ludvig Holberg while functioning as a one-man affair where Seyler dominated all decisions.
At the Gotha court between 1774 and 1775 Abel Seyler commissioned Bohemian composer Georg Anton Benda to write several successful operas including Ariadne auf Naxos, Medea, and Pygmalion. At its debut in 1775, Ariadne auf Naxos received enthusiastic reviews throughout Germany and Europe and is widely considered Benda's best work.
Abel Seyler was forced to leave his position in 1781 after an unfortunate incident involving his wife's jealousy during rehearsals with Elisabeth Toscani. He slapped her face in response to repeated insolent remarks which led Dalberg to decide to retire Seyler with a pension to restore peace.