Short answers, pulled from the story.
Abel Seyler (1730-1800) was a Swiss-born merchant banker turned theatre director, regarded as one of the great theatre principals of 18th century Europe. He was described as "the leading patron of German theatre" in his lifetime and credited with introducing Shakespeare to German-language audiences, pioneering a more realist style of acting, and promoting the concept of a national theatre and serious German opera.
Seyler & Tillemann went bankrupt in the wake of the Amsterdam banking crisis of 1763 with 3-4 million Mark Banco in debts. The firm had engaged in aggressive bill-jobbing and speculation during the Seven Years' War, was effectively insolvent by August 1762, and collapsed when the Amsterdam house of De Neufville failed. Civil litigation ran from 1763 to 1773 and reached the Imperial Cameral Tribunal.
The Hamburg National Theatre was an idealistic attempt to establish a publicly funded national theatre, of which Abel Seyler became the dominant force from 1767. It employed Gotthold Ephraim Lessing as the world's first professional dramaturg. Lessing's reflections on the theatre produced Hamburg Dramaturgy, a collection of essays that defined the field of dramaturgy and gave it its name.
The Seyler Company commissioned Alceste, composed by Anton Schweitzer with a libretto by Christoph Martin Wieland, which premiered in Weimar in 1773. It is considered the first full-length serious opera in German. Seyler also commissioned Georg Anton Benda's Ariadne auf Naxos, which debuted in 1775 to enthusiastic reviews across Europe and is widely considered Benda's finest work.
Abel Seyler's wife Sophie published the Singspiel Huon and Amanda (also called Oberon) in 1789. A version with new music by Paul Wranitzky became the first opera performed by Emanuel Schikaneder's troupe and established that company's tradition of fairy-tale operas. Sophie Seyler's Oberon is regarded as one of the primary influences on the plot and characters of The Magic Flute, which Mozart and Schikaneder produced two years later.
On the 25th of June 1774, Abel Seyler and Konrad Ekhof founded the first masonic lodge in Gotha at the Gasthof Zum Mohren. Originally named Cosmopolit, it was renamed Zum Rautenkranz in honour of the ducal family. Ekhof became its first Worshipful Master and Seyler the First Warden. Reigning Duke Ernest II of Saxe-Gotha-Altenburg and his brother soon joined the lodge.