Full documentation in the plugin folder! (documentation.html) Or here: Documentation
Sorry, I don't know. Try to uninstall/install the plugin or just pick up the image in the svn repository.
First: do you have the latest version of this plugin? Second: did you find the settings page, create your Twitter plugin?
Since the v1.1.3, the cache system prefers keep your old tweets instead of displaying a error message due to a lack of tweets inside the Twitter flow. It's a kind of security: old tweets are better than error message :)
You can use lot of CSS classes and filters to help you in you quest :) See the documentation.html files inside your plugin folder !