Short answers, pulled from the story.
John Lennon wrote the song about his love for Yoko Ono. Lennon told Rolling Stone that the "She's So Heavy" title referred to Yoko, explaining that when you're drowning, you don't speak in formal sentences. You just scream.
The basic track was recorded at Trident Studios on the 22nd of February 1969. Overdub sessions took place on the 18th and the 20th of April, and on the 8th and the 11th of August 1969, with the final mixing session on the 20th of August 1969.
John Lennon instructed recording engineer Geoff Emerick to cut the tape at the 7:44 mark rather than fade it out. Emerick had expected a fade. Lennon chose the abrupt cut during the final editing session, ending the song and side one of Abbey Road in mid-repetition.
The 20th of August 1969 was the final occasion all four Beatles worked together in a studio. They gathered that day to mix I Want You (She's So Heavy) for Abbey Road.
John Lennon played lead guitar and Moog synthesizer, Paul McCartney played bass guitar, George Harrison played electric rhythm guitar, and Ringo Starr played drums, congas, and wind machine. Billy Preston contributed Hammond organ.
Critics have credited the song with predating doom metal and stoner rock. Guitar World ranked it 34th among the fifty heaviest songs recorded before Black Sabbath, and Classic Rock noted it predated Black Sabbath's creation of doom rock by several months.