Short answers, pulled from the story.
Paul I was assassinated on the night of the 23rd of March 1801 at Saint Michael's Castle in St. Petersburg. A band of dismissed officers, including General Levin August Count von Bennigsen and General Vladimir Mikhailovich Yashvil, dragged him from behind drapes in his bedroom, attempted to force his abdication, and then strangled and trampled him to death after he resisted. The official cause of death was declared apoplexy by the court physician James Wylie.
The conspiracy against Paul I was organized by Peter Ludwig von der Pahlen, Nikita Petrovich Panin, and José de Ribas. It was allegedly financed by Olga Zherebtsova, using funds from her lover Charles Whitworth, the British ambassador to Russia who had been recalled by Paul in 1800. De Ribas died in December 1800, which delayed the assassination.
The Pauline Laws established strict male-line primogeniture for succession to the Russian throne, meaning the crown would pass to the next male heir in order of birth. Paul created them partly out of fear that Catherine the Great's will would bypass him and leave the throne to his son Alexander. These rules governed the Russian throne until the end of the Romanov dynasty.
Paul I became Grand Master of the Knights Hospitaller on the 24th of November 1798, after the Priory of St. Petersburg elected him following France's occupation of Malta. He had been fascinated by the Order since childhood and had relocated the Priories of Poland to St. Petersburg in January 1797. His election as an Orthodox sovereign to lead a Catholic order was controversial, and the Holy See delayed its approval.
Paul I abandoned the Second Coalition after the alliance with Austria collapsed in October 1799, following Austria's refusal to restore the Italian monarchies and its perceived betrayal of Russian forces in Switzerland. Relations with Britain then broke down over Malta, neutral shipping rights, and the treatment of Russian troops after the Holland invasion. Paul came to see Napoleon's France as a more conservative and compatible power after Bonaparte became First Consul.
Paul I and Catherine the Great maintained a distant and mistrustful relationship throughout her reign. Catherine never invited Paul to share power, favored her own lovers over him, and by 1787 appeared to have decided to bypass him in favor of his son Alexander as her successor. Paul openly criticized her policies in a document called Reflections and spent years away from the Imperial Court at his private estate of Gatchina Palace.