I have a wide variety of Slackware systems, with a wide range of displays, and physical configurations.

Generally, a user remains constant across machines, and has access to their /home directory via NFS. The problems I am trying to solve include:

-different desktops does not always run the same Slackware or for that matter the same kernel
-the KDE layout desired is different for different desktop machines (and also for different users)
-video configurations vary substantially (I haven't been able to statically lock these in except to run the krandr tool. It appears that the old way of setting up Xorg.conf doesn't always drive the resulting display

I'm looking for general pointers, ideas as to how others have addressed this problem, etc. Thanks.

What do the mean by "KDE layout desired is different for different desktop machines (and also for different users)"?

The KDE applications store most of their data and settings in a hidden directory within the the home directory (.kde or .kde4, depending on the distribution). Configuration is in .kde/share/config, and some of the data in .kde/share/apps. Other data is stored in .local/share.

Do I assume correctly that you want to share the data and most of the settings (of all the various KDE applications) between the different machines?

Do I also assume correctly that you will need to deal with different versions of KDE Plasma and the other KDE applications?

Your assumptions are valid. One particular problem I have is that different screen configurations on different machines cause some havoc, in that screen layouts are different and the panel toolbox fits differently.

It would be nice to have a different layout possible in some of the machines.

I suppose that could be done with some scripting, with something like a .kde.desktop1 > .kde at login time.

Again, I am exploring to see what might be possible, after having looked at the KDE docs.