Yep, an accurate thermometer is pretty important. I had to bit the bullet and get a waterproof one.
Most folks mash at around 1.25 quarts per pound of grain. Then you have to figure for grain absobtion and add enough water at the end of the mash so you get about 1\2 of needed wort.
If you have to cool the mash use ice cubes, they work better without adding a bunch of water. It is easier to cool than to heat up the mash with batch sparging.
I vorlauf about 2 quarts. It's plenty more than needed but I am assured that the runnings are clear.
On the 2nd sparge my water temp is 185-190 and I don't get close to 170 in the mash.