The https://help.ubuntu.com/community/MetaPackages is telling:
kde-base: This metapackage includes the nucleus of KDE, namely the
minimal package set necessary to run KDE as a desktop environment.
This includes the window manager, taskbar, control center, a text
editor, file manager, web browser, X terminal emulator, and many other
programs and components.
There has been package naming changes. I think that this is the current nucleus of the KDE:
kde-baseapps
Description: base applications from the official KDE release
(meta-package) ... This package provides core applications for the KDE
4 desktop.
The kde-baseapps is depending:
- dolphin
- kde-baseapps-bin
- kdepasswd
- kfind
- konqueror
- plasma-widget-folderview
These may be useful:
plasma-desktop
and then install whatever applications you want.