#1 - It depends upon your location rules.  "ZAC ZC -L" will list all of the "Content" Servers for a location.  Devices will check the servers in order for the needed content.

For Number 2, old unneeded content is cleaned up nightly on primaries, not every 3 months.  Satellites it is more about the replication schedule. There are many ways to reduce content overhead.

• ZCC->"Bundle, Policy, Content":  Set Old Bundles to retain a limited number of versions.  Perhaps 1, 2, or 3.  Keeping many old versions can cause the content repo to grow if the different bundles have different content.  If the content is the same across bundles, there is no additional overhead. (I believe this will process overnight for older bundles.)
• Delete old System Updates.  Even the ZENworks 20.1 System-Update can be deleted if you are not still upgrading devices.  "ZMAN SUDU" with the "FORCE" option can delete older system updates that are no longer visible in the ZCC.  System Updates can be fairly large.
• Flag certain bundles to not replicate to satellites that are rarely used 

After doing the above......

www.novell.com/.../b74pt40.html

Look for the content commands for "ZMAN" to clear content on the primary "zman ctc" or to force replication on the satellite which will also remove old content.