I am confused on some of the basic's. Hopefully these won't make me look too foolish.

When you preheat a mash tun, does it matter what temp the water is? What temp are you preheating the mash tun to?
On my first AG batch I didn't preheat my mash tun, it was around 100F outside, and I hit my mash in temp. The second and third AG batchs I did preheat my mash tun with around 170F water, temp was in the 60'sF outside, and my mash in temp was way low. On my last batch, I preheated my mash tun with boiling water, outside temp was 42F, and my mash in temp was way high. I think I am making things harder than they need to be.
When you sparge with 168 - 170F water, is this the water temp or mash temp? I thought I had read that you needed to raise the mash temp to 168 or above to stop the enzyme activity, but other things make it sound like you just sparge with 168F water.
Thanks in advance!
Dano