Brew,
1. the particulars will depend on your own system, but I do the same as Richard: I know I need approx 20 degrees F above the desired mash temp and about 17 degrees above the desired sparge temp, with adjustments made for grain mass, and from there fine tuning is rarely needed, but if so is done with either really hot, or really cold water in small amounts.
2. Sparge temperature needs to be hot enough to kill off the mash enzymes and cool enough to not extract undesirable flavours from the grain. I don't really know the upper limit, but the lower is about 168F. At boiling, water will extract bitter tannins from grain.