1) Astronomer
2) It has an elliptical orbit around the sun, and having measured its course that orbit can be calculated with very precise accuracy; and in this case it is a big-ass ellipse that takes 80,000 years to do one lap. (80,000 years ago wasn't when it first appeared, that is the last time it appeared locally)
3) Collisions: to quote Douglas Adams: "Space is BIG. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space". The chances of two objects bumping in to each other really aren't that high, so any given comet can circulate for a very long time before it hits something.
4) No, I haven't seen it, neither will I look - all celestial objects are a marvel, I don't really consider any one to be more special than any others. Saves me having to run out and check whenever something new happens. I will, however, look up if something is on a collision course!