Blog Summary produces a semantic, hAtom-enabled list of the latest blog post excerpts with the shortcode `[blog-summary]`.
It inserts list of your latest blog posts where the shortcode
[blog-summary] is used on a post or page. Nothing more, nothing less.
Yes. You can specify shortcode attributes to customize the HTML elements that group the output. See the plugin page for more information on attributes that this shortcode will parse.
This plugin uses the WordPress function
the_excerpt to produced a short 'summary' of your latest blog posts. You can specify your excerpt in the post editor. See Writing Posts in the WordPress Codex for more information.
It could, but you will have to modify the plugin. Search for
the_excerpt and modify accordingly, but you're on your own for this.
The Sandbox is a design-less theme for WordPress that has a highly extensible XHTML structure powered by these nifty functions that create semantic classes, i.e., classes that have meaningful names related to the content. For more information on this, see the Sandbox documentation.
No, it is not required. But its advanced class-generating functions are supported by this plugin.