More information than standard "Site Details", also to be available as tokens
I wrote a tutorial on most of this: http://www.jaypan.com/tutorial/drupal-8-extending-core-configuration-extending-core-forms-and-overriding-core-routes

I didn't get into creating tokens for the new items, but you can do it by implementing hook_token_info_alter() and declaring the new tokens as part of the site tokens, and implementing hook_tokens_alter() to set the values from the config you create following the tutorial.