Brian Eno: Provides "Enossification", which apparently refers to sound treatments he did on some songs. He may also have let the band borrow some equipment.
Fake American: A half-Puerto Rican street kid from New York City would be unlikely to refer to money as "notes and coins". But he does anyway in "The Grand Parade of Lifeless Packaging". And in the next song ("Back in N.Y.C.") he says "progressive hypocrites" instead of "liberal hypocrites" — "progressive" wasn't a common term in America until 15 or 20 years later (or several decades earlier, but hey).
Sequel First: Due to a late injury to Steve Hackett during rehearsals and the necessary switching of venue dates that followed, the American leg of the The Lamb Lies Down On Broadway tour was scheduled to happen before the album itself had even been released in the US. The band ended up playing the entirety of the album to audiences who hadn't heard it yet and certainly weren't expecting anything like that.
For starters, Peter Gabriel insisted on writing all of the lyrics himself, feeling that a consistent story would be necessary. At the time, his marriage was in trouble and his newborn daughter was in an incubator. This led to most of the music being written in his absence by the rest of the band.
The location of the recording, Mick Jagger's Stargroves mansion, which was often a favorite recording location for Led Zeppelin, turned out be be rundown, infested by rats and was believed by band members to be haunted. The group had very little sleep, and what was supposed to be a way of solidifying group unity actually led to stress and strain for the band.
Arguments over included songs and lyrics. The other members of the band would occasionally rewrite Gabriel's lyrics to better fit their music, and Gabriel wrote several songs on his own (to bridge already-written sections) without the rest of the band's input (one of them, "The Carpet Crawlers", would be a live staple for the post-Gabriel band). Gabriel also ran into writer's block with "The Light Lies Down On Broadway", leaving Banks and Rutherford to write both music and lyrics.
In the middle of the album sessions, Gabriel received an offer to work with William Friedkin on a movie screenplay, and couldn't see why the rest of the band thought leaving in the middle of an album session might be a bad thing. When the others found out, they told their manager Tony Smith, who had to call Friedkin and get him to back off, which led to discontent on Gabriel's part. Gabriel made it clear he was leaving the band, although he stayed to do the live tour. The film project never came to pass because of that.
Due to stress from being creatively sidelined on the album and his own failing marriage, Steve Hackett snapped a wineglass in his hand during rehearsals, injuring tendons in his thumb and delaying the start of the tour. After some juggling of venue dates, this meant the first leg of the tour was to be in America, where the album hadn't been released yet. Ticket sales went "meh." Hackett would record his first solo album (Voyage Of The Acolyte) shortly after the tour, and would leave the band three years later, in 1977.
The live show was troubled by faulty equipment (including the slides meant to visually display the story). The band performed the entire double album, and only performed older, more recognized material in encores. Gabriel eschewed his trademark costumes for most of the show, and when he donned them for the second half, the overly elaborate designs prevented him from getting a microphone near his mouth, rendering the lyrics incomprehensible.
In the end, the album tanked on the charts, was savaged by critics and fans alike, and the band lost their ass on the tour, as well as their lead singer, nearly causing a break-up. For obvious reasons, almost all the members of the band treated it as an Old Shame for many years, only beginning to warm up to it much later when they could put the stress of creating it behind them. (As a sort of belated consolation, the album did eventually go gold.)