Short answers, pulled from the story.
Marshal of the Empire was a civil dignity, not a military rank, established by sénatus-consulte on the 18th of May 1804 during the First French Empire. It was the highest-standing among the grand officers of the Empire, outranking every military grade in terms of prestige, and entitled its holders to a distinctive baton, special court etiquette, and in many cases a ducal or princely title.
Napoleon appointed a total of 26 Marshals across his reign from 1804 to 1815, though the number active at any single moment never exceeded 20. The first promotion in 1804 created 18 Marshals at once; six further promotions followed, with the final one taking place in 1815 before the Hundred Days.
Joachim Murat, who had married Napoleon's sister Caroline, became King of Naples in 1808. Jean-Baptiste Bernadotte became Crown Prince of Sweden in 1810 and King of Sweden in 1818; the source notes he is the direct ancestor of the current Swedish royal family.
The baton was cylindrical, fifty centimetres long and four and a half centimetres in diameter, made of wood and covered in dark blue velvet. It was decorated with golden eagles or honey bees, both Imperial symbols. The Marshal's uniform, including his four silver stars, was established by decree on the 18th of July 1804 and designed by painter Jean-Baptiste Isabey and designer Charles Percier.
Three Marshals were killed in action or died of battle wounds: Jean Lannes, who was mortally wounded at Aspern-Essling on the 31st of May 1809; Jean-Baptiste Bessières, who died near Lützen on the 1st of May 1813; and Józef Poniatowski, who drowned at Leipzig on the 19th of October 1813 after serving as a Marshal for only three days.
Józef Antoni Poniatowski, a member of the House of Poniatowski, was the only Marshal of Napoleon's Empire who was not French. He received the baton in 1813 and was elevated in the sixth promotion alongside the Battle of Leipzig, where he drowned during the retreat after just three days as a Marshal.