I can't wear more than 3 layers. Feels like a straightjacket to me. That said, I have no problem with wool next to my skin so I usually don't need to worry about my layer order.

My spring/fall/winter uniform consists of a wool baselayer, a wool or fleece midlayer, and a wind jacket. If it's really cold, I throw a synthetic puffy vest in there. Wool works great as a midlayer, but it's heavier than fleece for its warmth. Fleece is lighter and warmer and goes great with a wool baselayer.