Short answers, pulled from the story.
Napoleon established the Kingdom of Westphalia in 1807 through a series of territorial mergers. The new state absorbed lands from Prussia, Hanover, Brunswick-Wolfenbüttel, and the Electorate of Hesse.
King Jérôme Bonaparte kept his court at the palace renamed Napoleonshöhe in Cassel. This arrangement placed the kingdom within the Confederation of the Rhine as a French client state.
The kingdom implemented Germany's first modern written constitution on the 15th of November 1807 which came into effect when Jérôme arrived in Cassel on the 7th of December 1807. All male residents gained equal rights under this new legal framework and serfdom ended immediately across the entire territory.
A contingent of 25,000 soldiers and 800 officers marched into Russia with Napoleon's army but only 600 soldiers and 18 officers returned from the campaign after its conclusion. Another 600 men defected to join the Russian forces during the retreat.
Prussian troops occupied Westphalia on the 26th of October after the French defeat at Leipzig. The kingdom dissolved completely when the status quo of 1806 was restored and most territories became part of Prussia except for Rietberg and Stolberg-Wernigerode counties.