For the most part with batch sparging, the mash pH/grain bed pH is somewhat set. It would take a lot to shift it, in my experience. Or at least I would not worry about it if I pretreat my sparge water with acid. I generally set my sparge water at a pH of approx. 6 if using tap water. With R/O water I do not worry about my sparge water pH. The grain bed is fairly resistant to large temp changes as well with batch sparging. I generally infuse a gallon or so, depending on the recipe, to get my 1st and 2nd runnings of equal volume. The water I add back for the second sparge is generally pretty hot. It is the grain bed temp, not the sparge temp that you want to monitor. So, if I mash low like at 148F, I may add 195F to 200F sparge water. If I mash warmer, say 154F, I generally add 185F-190F sparge water. I mash in a converted cooler and check the grain bed to make sure the temp is in the 168-170F range. But, this is my system not yours and I know my systems parameters. Every brewer and system is different so you have to find out what works best for you. Definitely, check your grain bed temps and periodically check your 2nd and if needed 3rd running pH to make sure that they don't start creeping up.