The 'Wp My Admin Bar' Plugin expands on the default WordPress Admin Bar, adding 3 new quick access menus.
A) It works with, all Multisite Setups (not multi-user at this time), and Standalone WordPress.org Installs.
A) Yes, you can access it via the Network Admin > Settings > Admin Bar
A) Yes! After you Network Activate the plugin, adjust the settings within the Network Admin. Then don't touch them again! After that, if a Website is missing a feature or needs a feature, access that websites admin bar settings page to adjust that Website only.
A) Yes!!! If you use Multisite use: Super Cache + Widget Cache. Non-Multisite setups use: Total Cache + Widget Cache - Wp Minify and DB Cache are optional plugins that may or may not work for you, depending on your setup, themes, and other junk.
A) No, disabling keeps everything in place. However, deleting the plugin (through the WordPress Admin) will remove all settings.
A) I'm not sure, however it's only one Website, setting it back will only take a few seconds.
A) No, not until you update the Network Admin Settings directly.