Short answers, pulled from the story.
West Virginia became the 35th state on the 20th of June 1863. President Lincoln signed the statehood bill on the 31st of December 1862, and the state took effect after voters approved the Willey Amendment on the 26th of March 1863.
Estimates have ranged widely across generations of historical scholarship. A 1989 study by James Carter Linger placed Confederate service at nearly 22,000, close to the 18,642 figure recorded by the Confederate Department of Western Virginia in 1864. A 1995 soldier-by-soldier count by the George Tyler Moore Center concluded that West Virginia contributed roughly 20,000-22,000 men to each side.
The Willey Amendment was a gradual emancipation clause attached to the West Virginia statehood bill by Senator Waitman T. Willey. Approved by voters on the 26th of March 1863, it freed no slaves during the war and only freed children at birth or as they came of age. Full abolition came when the West Virginia legislature acted on the 3rd of February 1865, eighteen months after statehood.
Both the Confederate government and the state government in Richmond refused to recognize West Virginia's creation in 1863. They regarded the Wheeling government as illegitimate and its territory as enemy-occupied Virginia, so Confederate military campaigns there were framed as efforts to liberate Confederate citizens rather than as invasions of a foreign state.
The B&O Railroad was central to West Virginia's Unionist character and political formation. Its construction in the 1850s brought thousands of northerners and immigrants to towns along its line. The Wheeling government's effective control was limited to the northern panhandle and the counties along the B&O corridor, and the railroad was also a prime Confederate military target throughout the war.
McNeill's Rangers were a Confederate partisan unit from Hardy County. In one of the final acts of the guerrilla war in West Virginia, they kidnapped Union Generals George Crook and Benjamin F. Kelley from behind Union lines and delivered them as prisoners to Richmond. The Confederate surrender at Appomattox ended their campaign.