Drupal 7 comes with a “Tags” taxonomy by default (if you do the regular install). This views export will create a block that lists the “Tags” with the number of content instances for each one. You can see it in action right here =>
The default admin theme Seven is really great… clean, direct and simple. However, I do find it a bit bland. I mean, yeah… its supposed to be sort of “boring” because its just a clean admin theme. But the light grey header really washes out the page. I’ve made a few tweaks to the theme over time in order to make it a bit “better” (imho).