What is the optimal temperature for making coffee, specifically in an AeroPress?
When making espresso with a machine, normally the ideal temp is around 200F. So I would most definitely not use cooler water.

175F is very hot for steaming milk--for me that would be way over-steamed and scalded. Most of the resources I've found say to steam to 150-160F.

I've actually found that even when the thermometer says 150F, it's over-cooked for my tastes. What I do now is go by feel. I steam in a stainless pitcher and keep my fingertips on the sides. When it's too hot for me to hold for more than a second or so, I stop.