Short answers, pulled from the story.
The Novgorod Republic existed from 1136, when the Novgorodians deposed Prince Vsevolod Mstislavich and began electing their own rulers, until 1478, when Ivan III dissolved the veche, removed the veche bell to Moscow, and imposed direct rule. Ivan III took more than four-fifths of Novgorod's land after the annexation.
The veche was Novgorod's popular assembly and the theoretical seat of supreme power in the republic. It elected the posadnik, the archbishop, and the tysyatsky, and it could invite or dismiss the city's princes. By the 15th century, estimates suggest no more than five to six thousand men held the right to participate in its meetings.
The republic's primary source of wealth was the fur trade. Novgorod served as the easternmost trading post of the Hanseatic League, supplying vast quantities of squirrel and other furs to Baltic merchants. The Lübeck company of Wittenborg alone exported between 200,000 and 500,000 Lübeck marks from Novgorod to Livonia in the 1350s. Silver, cloth, wine, and herring were imported from Western Europe in return.
Alexander Yaroslavich, later known as Nevsky, was left in Novgorod as a teenager around 1235 by his father Yaroslav of Suzdal. According to Russian sources, he defeated a Swedish army at the Battle of the Neva in July 1240 and drove back German crusaders at the Battle on the Ice in 1242. He was also the figure who allowed Mongol tax-collectors into the city in 1259 and punished officials who defied his authority as the khan's representative.
Over a thousand birch bark manuscripts have been recovered from Novgorod since archaeological excavations began in the 1950s, with scholars estimating as many as twenty thousand still remain underground. The texts include business letters, religious documents, and personal notes written by men, women, and children across all social classes. The oldest surviving Russian manuscript was also found in Novgorod: wax tablets bearing Psalms 67, 75, and 76 from the first quarter of the 11th century.
The boyars were the highest hereditary nobility of Novgorod, and the historian Valentin Yanin concluded they formed a closed group of families descended from a small number of ancestors. By the 14th and 15th centuries, more than half of all privately owned land in the republic was concentrated in the hands of roughly thirty to forty boyar families. The offices of posadnik and tysyatsky remained firmly in boyar hands throughout the republic's history.