Abe Vayoda said:I remember reading an interview with Bob Gale where he addressed the problem of future Biff altering the past. It was something along the lines that is takes time for the future to catch up to the changes in the past. I also remember seeing a deleted scene where future Biff is "dying" because the changes of the past affect him first.
I don't think so, in the original theatrical release there wasn't a "to be continued". It was added later.
Yeah there was no plan for sequels at the time the first movie was released. In the DVD commentary Bob Gale says, "If we had known there was going to be a sequel we never would have put the girl in the car."