Wow... that sounds like a clear threat was coming at you. I think you handled it pretty good considering the circumstances.
The only thing I might have done that you did not mention was to observe in order to have an accurate description to give the cops, then I'd have called the cops.
Those natural alarms going off can usually be trusted, and if yours were ringing, odds are really great that your heeding them kept you safe.
Had this happened to me, the only possible difference might be how close he got before I challenged him to keep his distance away from me, and my pistol would not have been on the seat, but on my hip. Since it was pretty obvious that he lied about needing jumper cables, I believe RAS existed for investigating his behavior. I'd have gotten the cops to check him out. You got off safely, but what about the next guy? Or the next woman? You know the type... folks who won't carry and aren't able to defend themself against an assault?
You done a great job and I applaud you for picking up on queues to a hinky situation. I don't think I'd have handled it much better myself.