System Center Configuration Manager can be used to deploy Modern/WS Apps.
But AFAIK, there isn't any builtin capability in Windows for auto-updating Modern apps at all - it requires an "agent" of some kind.
Even the Windows Store app itself is kind of an agent, in that the Windows Store app would communicate with the Windows Store webservices to check for app updates.
You *might* be able to implement something a little like "auto update" using scripting, e.g. startup scripts in GPO, that could perform sideloading tasks.
For the "no expiration" requirement, this is determined by the signing certificate approach you choose, and the validity period of the certificates used.
http://blogs.msdn.com/b/windowsstore/archive/2012/04/25/deploying-metro-style-apps-to-businesses.aspx
this is an older article (some things have changed since Win8.1 and Win8.1u1 were released), but it provides an overview.
http://channel9.msdn.com/Events/MMS/2013/DC-B320
Windows Store Apps: Enterprise LOB App Deployment Scenarios
this is a highly recommended video by Windows Deployment senior guru Michael Niehaus, which covers lots of great deep