Is there a safe way to move the /Users folder to a separate volume/drive?

May be able just create a simlink to the /User directory.

To do this, open up Terminal and enter:

cd [SeperateDrivePath*]
ln -s ./Users /Users

You'll want to move your original Users folder out of the way (rename it or move it or whatever).

*Where [SeperateDrivePath] is the path to your volume just underneath the cloned /Users folder. Probably something like /Volumes/Some Hard Drive Name/. In this case, your clones /Users should exist at/Volumes/Some Hard Drive Name/Users.

The best way to do this is probably to setup /Users as an automounted partition, with all your home directories in the root of that partition. I am going to assume you have already copied over the home directories properly (with permissions enabled). Now you just need to add the volume to /etc/fstab. Assuming the parition is named Users, you add a line like this:

LABEL=Users /Users  hfs rw,auto

Instead of using the volume name you could also use the volumes GUID if you know how to find it, which would be slightly more reliable (it would prevent mishaps if you ever inserted another volume with the name Users. That would looks something like:

UUID=DF000C7E-AE0C-3B15-B730-DFD2EF15CB91   /Users  hfs rw,auto

You can find more information in man 5 fstab. Be warned, that manpage is mostly about the programming interface for fstab, but also goes into the file. Unfortunately it does not go into all the options available, there really appears to be no good documentation for it, but this should give you enough to get what you want done.