Probably my single favorite is:
American Military Equipage, 1851-1872: A Description by Word and Picture of What the American Solider, Sailor, and Marine of These Years Wore and Car by Frederick P. Todd
It is out of print but can sometimes be found. It explains your particular questions.
Two others that I have found very useful are:
The Horse Soldier 1851-1880: The Frontier, the Mexican War, the Civil War, the Indian Wars
by Randy Steffen
Army Blue: The Uniform of Uncle Sam's Regulars, 1848-1873
by J. Phillip Langellier, John P. Langellier
Osprey Publishing puts out an extensive series of small books on uniforms by topic and era. They include a collection of photographs and usually some colored drawings. John Langellier is particularly prolific in his books on CW-era uniforms.