Winter Time - Cold Start Noises - Suggested Oil? 98 GT

So, I live in Wyoming...and its HELLA cold already.

I decided to drive my GT today as there won't be many more days where its warm enough to do so. And really, it can be cold, but the roads have to be super decent as my tires wont allow even a tiny bit of ice.

I went to fire up the Mustang this morning (In the upper 20's) and I hear this scratching noise coming from what I could tell, was the upper part of the engine. (Hard to tell when your in the car). I figured, cold start, oil circulation.

After about a minute it went away.

Obviously, I need to start and run the car once a month while its cold just to make sure it doesnt sit and go funky. But what kind of oil should go in it? The engine cap has 5W-20 on it...which is pretty damn thin.....but is probably perfect for winter.

Ideas?