Gotcha on the powerderd milk. Wasn't sure if it was a "don't have milk available" OR, "Powdered milk is better for baking", that's why the question, I thought I was missing something using powdered milk. But it's a GREAT idea, I also drink either Soy (Silk) or Coconut (Silk) or Almond (also Silk brand) milk, we only keep half and half in fridge for coffee. WE often have to run out to get a quart of milk when required for cooking... I should get some powered milk to keep in cabinet...
I could give you a conversion for it, I never actually mix up the milk I just toss the water and powder into the recipe. Don't want to mix it up and let it sit in the fridge.
Got to searchin for Sourdough info.... WOW, lots of great info about sourdough online. Ordered a free starter from Carl Griffith's 1847 starter still going.... LOVE Sourdough pancakes!