Burned-out after years of doing development work around the world, William Powers spent a season in a 12-foot-by-12-foot cabin off the grid in North Carolina, as recounted in his award-winning memoir Twelve by Twelve. Could he live a similarly minimalist life in the heart of New York City? To find out, Powers and his wife jettisoned 80 percent of their stuff, left their 2,000-square-foot Queens townhouse, and moved into a 350-square-foot "micro-apartment"...