Good for you getting ot there and giving it a go.
1. Only you know how far you can ethically make the shot, every time.
2. If you can see their head, they can probably see you draw, even from "behind." If you can draw when they stretch out to gobble, you might be able to get away with the movement since their head is moving rapidly. If they are fanned out, wait until their head is hidden by their fan.
3. Sometimes as far as he can hear her, sometimes he won't come from 100 yards, depends on him, conditions, and the terrain, don't try calling them downhill usually. Sound travels diffently in the open or treed areas, over flat or hilly ground, in the calm or wind.

Hope some of this helps.