I start out with the bare minimum of polygons that I need to make an outline of the prop. I go back later to divide them up. If you are making a static prop that you don't intend to morph, you don't need a lot of polygons. You also don't need a lot of the prop is going to be used as a background piece most of the time. If it's something you might morph, you want to add more polygons, to give finer control over the morphs. And if you're doing something like dynamic clothes, you need more polygons to help keep dynamic simulations from choking. If it's a prop that needs to be ultra real close up, then you'll need more polygons. The more polygons you have, the more memory your prop takes up, and in Poser memory is at a premium. Thus, fewer is better, so I think it's better to start low and then add some divisions if you need to.