The Plane of Air is largely inhabitable and not too unpleasant, if you find some ground to stand on. There's cities on rocks and so on. The Plane of water has bubbles of air that are more or less inhabitable. If you have air breathing, the plane of water is for the most part full of life. The plane of earth has cave systems, including cities. Fire, not for the most part, though there is the City of Brass, which is marginally liveable.