Short answers, pulled from the story.
The Kingdom of Italy was officially born on the 23rd of May 1805 when Napoleon I received the Iron Crown of Lombardy at Milan Cathedral. This event transformed the Italian Republic into a client state under his direct rule and marked the start of its existence until 1814.
Eugène de Beauharnais served as viceroy of the Kingdom of Italy starting from its inception in 1805 while he was only twenty-four years old. He commanded the IV Corps invading Russia in 1812 and attempted to be crowned king after Napoleon abdicated in April 1814 before being exiled to Bavaria.
Austria ceded eastern Venetian territories including Istria and Dalmatia to the Kingdom of Italy through treaties signed on the 26th of December 1805 and the 14th of October 1809. The Duchy of Guastalla was also annexed on the 24th of May 1806, and border adjustments moved the frontier to the Isonzo river by October 1807.
The Kingdom of Italy provided exactly 30,183 soldiers to military campaigns between 1808 and 1813 during the Peninsular War and Russian invasion. Only 8,958 men returned home alive while others fell to combat or disease due to high casualty rates exceeding ninety percent in some units.
Napoleon abdicated both thrones on the 11th of April 1814 triggering immediate political chaos that ended the Kingdom of Italy. Austria occupied Milan on the 28th of April and the Treaty of Paris signed on the 30th of May annexed remaining territories to the Austrian Empire as the Kingdom of Lombardy-Venetia announced publicly on the 12th of June.