What height above floor or above table should I be?
What will the table be used for? Will kids be standing making models of volcanoes? In that case hang it higher. Are people always seated eating at the table? Then you can hang it lower.
I think this is personal preference, and, as Tribble.... says, it depends on use. You could also consider looping the cable decoratively, so you could potentially adjust the height later if you wanted to. I've attached an image of a light we installed as an example.
We placed ours 1 metre from the table , it creates an intimate cosy feel without being in the way.