If I am doing regular borders, I usually sew the sides on first, then the top/bottom. I do the same with each border. Generally, I put a narrow inner border and wider outer border. I often use the same fabric as inner border for the binding. As for measuring, I measure the quilt in a couple of places, cut the border, match the center and ends and ease in if I need to along the way. I have never had wavy borders this way. Also I usually cut my border fabric lengthwise so I don't have to piece it.