I don't think the actual urls matter. In terms of site structure, I actually don't recommend having too many nested folders/directories if you don't have a lot of inner pages. I see a lot of sites with category and subcategory pages with just 5-10 links in each. Google won't crawl that deep if your site is new. and the deeper a page is, the less important Google deems it (based on flow of internal Pagerank).