Common /home Across Distro Versions

[jbk-SkCWf5sxpj0sV2N9l4h3zg at public.gmane.org (jbk)]

I have a desktop that the family and guests share in the kitchen. The 
Fedora Distro is installed along with a virtual machine tailored to each 
of the users needs. I need to migrate my users to F12 from F10. This 
usually takes a week to a month to do because I want to make sure that 
most things work. I have allocated distinct partitions that I rotate 
between distro versions. So in the past I would carefully recreate each 
user in the new version paying attention to matching each UID and GID 
exactly, copy  the users home to the new home preserving date and 
ownership of files. This is a cumbersome and time consuming process. To 
streamline this process I want to create a separate home partition and 
move the users homes to that then delete the old homes and remount to 
the root partition. I have several questions that I need your help.

   1. Can I copy the /etc/passwd, /etc/shadow and /etc/group fields for
      each user from F10 to F12 into the same named files?
   2. What is the sequence of commands in tar to easily move the home
      directories preserving ownership and dates?
   3. What are the other critical administrative tasks that I should be
      aware of in this process?

Jim K-R