Nothing under. They are comfortable enough for me. Well - to be honest, I do have Dainese Fulcrum C2 boots that come up mid-calf, and so the lower 1/4 of the pads are on top of my boots.
Normal size pants - none of those "skinny jeans" for me! The leg seems to fit fine as-is. I love the Duluth gear, being a man of "stature" with big thighs and calves, and their jeans/pants just fit fine. Even with the pads underneath!