The required sparge water temperature depends on your equipment and methods.
You want to get the grain bed up to 165 - 170F. If you're batch sparging, I would start somewhere in the 175 - 180 area, and measure the temp of the grains after adding the sparge water, mixing, and letting it stabilize. If it's a bit low, you know that you need to heat the water a bit more the next time, but it should be fairly close.
And yes, the grains will be fully saturated during the mash, so adding x gallons of sparge water will deliver approximately the same volume of wort (A tiny bit more actually as the wort will contain the sugars rinsed from the grain as well as the water).
-a.