WordPress Blog and SEO

I doubt your URL structure will matter much for SEO. For more advice on this you can ask a question on the Pro Webmasters Stack Exchange site.

As Chip said you can change the Posts page under Settings → Reading to move your post index to http://example.com/blog/. The Front page is what people will see when they go to http://example.com/, and it should be one of your Pages.

The second step is to prefix all blog posts and category archives with /blog/ too. To do this, go to Settings → Permalinks and prepend /blog/ to your Custom Structure, so it becomes /blog/%year%/%monthnum%/%day%/%postname%/.