You can certainly use the Sharp for distance measuring and object avoidance. If you angle it downward, you can even write code to detect walls and drops (like the edge of a desk). In regard to learning how to use the Arduino programming language, there is no shortage of online tutorials and books, as well as printed books and more. It’s a bit dated, but still valid (9 lesson series):
You could possibly use a sharp IR sensor to track a line, but it’s really best to have at least three sensors, since only one sensor doesn’t tell you which side it’s slipped off - it just tells you “line” or “no line”.
Regarding the arm, why not? Go for it!