A child theme is a way to make changes to a WordPress theme without making changes to the main theme, the parent theme. Instead of re-applying the changes every time there’s an update, it’s simpler to keep the changes in what’s known as a child theme.
The new default theme Twenty Ten makes it easy to change the header or the background. A custom menu is built into the theme. You might want to tweak the CSS to get the spacing just right.
One needs to consider how a site will look on a mobile device. WordPress Mobile Pack is an easy way to switch a blog to a mobile theme when viewed on a mobile phone.