Short answers, pulled from the story.
The word divan traces back to Sumerian "dub," meaning a clay tablet, passing through Akkadian, Elamite, Old Persian, and Middle Persian before entering Arabic. English first recorded it in 1586 with the meaning "Oriental council of a state." The variant form dēvān survives in Tajiki Persian today.
The first dīwān was founded by Caliph Umar in 636/7 CE or, more likely, in 641 CE. It listed the warriors of Medina who participated in the Muslim conquests and their families, used to calculate salary payments in coin or rations. Al-Mughira ibn Shu'ba established a similar register in Basra during his governorship from 636 to 638.
The long cushioned seats built along the walls of Middle Eastern council chambers were also called divan. That sense of upholstered seating passed into European languages as a word for furniture. The same root, by a different route, gave French the word douane and Spanish the word aduana, both meaning "customs house."
The Divan-ı Hümayun, also called the Sublime Porte, was the council of ministers of the Ottoman Empire. It was presided over by the Grand Vizier and included the other viziers, the kadi'askers, the nisanci, and the defterdars.
Under the Abbasids, the number of dīwāns reached its peak in the 9th to 10th centuries. Caliph al-Mahdi (r. 775-785) introduced a control bureau for every existing department. In 913/4, the vizier Ali ibn Isa established a separate department for charitable endowments. The 11th-century scholar al-Mawardi described the central control bureau as "the guardian of the rights of bayt al-māl and the people."
"Dewan" is the Malay cognate of the Arabic dīwān and is the standard word in Malay and related languages for a legislative chamber. The Dewan Perwakilan Rakyat is Malaysia's Chamber of People's Representatives.