Multisite questions

  1. Yes. Use the Domain Mapping Plugin.
  2. Plugins can be enabled network-wide, or on a per-site basis. You can choose whether or not to give site admins the capability to activate/deactivate Plugins. Plugin settings are on a per-site basis.
  3. The Network Administration handles updates to core, Plugins, and Themes, and automates updating the database tables for each network site, when applicable.