Origins of the Movement: When did it form and who formed it?
The question of when goth started as a definite subculture is generally unanaswerable, but I'm going to try.
The term "gothic" for individual bands was around in 1979, and there were signs of an emerging musical movement by early 1981, when Abbo inadvertently tagged it "gothic", but goth as an identifiable movement in terms of both music and fashion didn't really appear till 1982. In July 1982, the Batcave opened: not only was this a major rallying-point for the London scene, but it attracted a lot of media attention, which in turn spread the idea of a new subculture around the country. In the wake of the Batcave, similar clubs opened around the country, and the Batcave itself went "on tour", giving goths outside London somewhere to gather.
Meanwhile, the musical movement had become equally high-profile and by February 1983 had acquired its own tag- though "positive punk" rather than "goth". Although the tag "goth" for both movement and music didn't become common until late 83, goth had pretty much become a major subculture by 1983, particularly with the success of "Ziggy Stardust" by Bauhaus (82) and "Dear Prudence" by the Banshees.
By early 1984, "gothic" had become a major tag, as evidenced in this quote from Pete Waddleton, the bass player in Play Dead, in an article in Zig Zag from April 1984:
"We're not gothic, we're not anything. People are always going to categorize you, especially the press. Well we don't care, any of us. Christ! Even I could write about bands, any idiot can do it. We're compared to the Sex Gang, Death Cult movement. THIS WASN'T A MOVEMENT. WELL, I MEAN . . . IT WASN'T A MOVEMENT TILL SOMEONE CALLED IT ONE!"