Short answers, pulled from the story.
At the outbreak of World War I in 1914, the Imperial Russian Army had a peacetime strength of approximately 1.3 million men, making it the largest peacetime standing army in Europe. Wartime mobilization raised this to 4.5 million troops, and a total of 15 million men served between 1914 and 1917.
Alexander Suvorov was a Russian general and military theorist active in the second half of the 18th century, regarded as one of the few commanders in history who never lost a battle. His victories span the Russo-Turkish Wars, the Kościuszko Uprising, and the Italian campaign of 1799, where he reversed Napoleon's gains of 1796-97. He left a lasting legacy of military doctrine for future generations of Russian commanders.
Count Dmitry Milyutin, as Minister of War under Alexander II, overhauled the army following Russia's defeat in the Crimean War. His reforms included reorganizing the Ministry of War, establishing permanent barracks, and on the 1st of January 1874 introducing compulsory military service for all 21-year-old males with a six-year active term plus nine years in reserve. The reforms also opened officer training to commoners, raising the share of non-noble officers from 4 percent in the 1860s to 44.6 percent by the 1890s.
Peter the Great introduced conscription in Russia in December 1699. The initial term of service was for life, which was only reduced to 25 years in 1793, and further reduced to 20 years plus five in reserve in 1834.
During World War I, Cossacks made up two-thirds of all Russian army cavalry, contributing over 500,000 men to the war effort. Of these, 200,000 were Don Cossacks and the remainder came from other hosts. They performed raids on enemy positions, policed deserters, and conducted a scorched-earth campaign during the Great Retreat of 1915.
The Imperial Russian Army did not collapse immediately after the February Revolution of 1917. In March 1917 it swore loyalty to the Provisional Government following the abdication of Nicholas II. The formal disintegration did not begin until early 1918, when its rebellious remnants evolved into the new Red Army.