with strike temp of 170 you can use that to preheat your cooler - 20° above your mash target should be more than enough to preheat and then allow you to hit your mash temp. you can use beersmith or greenbay rackers to calculate your target temp before you dough in if you haven't already.
also make sure you stir really well and don't just dump in the entire grain at once - you wanna make sure there are no dough balls (clumps of dry grain)
keep a pot of boiling water near by as well as some cold/ice water near so you can use a Little at a time to hit your temp - key is a little at a time, you can also stir for a bit longer if you are only a few degrees too high
sounds like you are batch sparging so you can completely drain the mash tun before adding the sparge water - you'll want your sparge water to be hotter than 170 before you add it, you want the grain bed and water to reach 168-170 to end conversion (mash out) you don't need to wait a full 20min, but you may want to start draining your runnings slowly and gradually open the valve up all the way if necessary
make sure you have a BIG starter - use mr malty or yeastcalc - likely to be around 3000-4000ml depending on your gravity
the diacetyl rest could happen sooner or later than 10 days, watch when your airlock slows down and take a gravity reading