Short answers, pulled from the story.
The Kingdom of Italy was founded on the 17th of March 1805, when the Italian Republic was transformed into a kingdom with Napoleon as its king. It lasted until Napoleon abdicated on the 11th of April 1814, a period of roughly nine years.
Eugène de Beauharnais, Napoleon's stepson, served as viceroy of the Kingdom of Italy. He was 24 years old when appointed. He commanded the IV Corps of the Grande Armee during the Russian campaign of 1812 and remained in command of Italian forces until he surrendered on the 23rd of April 1814.
At its peak the Kingdom of Italy covered 84,000 square kilometers and had a population of 6.5 million. At its maximum territorial extent it comprised 2,155 comunes and approximately 6,700,000 inhabitants.
Between 1800 and 1812, the Kingdom of Italy supplied 200,000 soldiers to Napoleon's armies. Including troops conscripted from Italian provinces directly annexed into the French Empire, the total reached 400,000 Italian soldiers who fought for France in the Napoleonic Wars.
27,000 troops from the Kingdom of Italy marched into Russia as part of the IV Corps under Eugène de Beauharnais. They fought at Smolensk, Borodino, Maloyaroslavets, and Krasnoi. Only 1,000-2,000 Italians survived the campaign, though they returned with most of their banners.
The kingdom used the Italian lira, introduced by Napoleon's imperial decree on the 21st of March 1806, with production beginning in 1807. The lira matched the French franc in size, weight, and metal content; the base silver lira weighed 5 grams.