Ghosthouse,
From the Playboy December 1984 interview (McCartney):
"Sgt Pepper was an idea I had, I think, when I was flying from LA to somewhereville. I thought it would be nice to lose our identities, to submerge ourselves in the persona of a fake group, us. We would make up all the culture around it and collect all our heroes in one place. So I thought, a typical stupid sounding name for a Dr. Hook's Medicine Show and Traveling Circus kind of thing would be Sgt. Pepper's Lonely Hearts Club Band. Just a word game really."
There is plenty written on the album. The best, IMO, are "The Beatles: 10 Years That Shook The World" and "The Beatles Anthology". They are my personal favs and I have a fairly extensive collection of Beatles resource material.