I would say about 4 or 5 ft at its narrowest.
No, it is an oscillating sprinkler. It can only go left and right but the controls on this sprinkler are what make it great. You can change the width and length and be able to cover great or small areas. This sprinkler is especially good for narrow areas due to the fact that you can change the width. I have a 10 ft wide and 30 ft length side yard and this is the ONLY sprinkler that works well. I also use it to water large areas.
3/4" or 5/8". Either one is fine.
The head is the same. The difference between the two is the material that the spike is made of.