First off, welcome to the forum and congratulations on making a commitment to cycling for health. Although you can do cardio with weights, cycling is far superior for this purpose. From your description of the areas where intend to ride, a SS setup seems to be a good choice. As far as bike choices, I would first try to work with a local bike shop before buying something online. Based on your weight, you are going to want a bike that can take wider tires, and some of the choices you have listed are limited to smaller tire sizes. Also, Some of those bikes like the Kilo TT are sold as fixed gears and do not have brakes on both the front and rear wheels. So, instead of a Kilo TT, I would get a Kilo WT, which is set up specifically as a SS, and has wider (700x32c) tires by default. As to materials, I'd just stick with steel in your price range.