I've always been updated to current and it's pretty stable (never had troubles yet). If you update KDE you should update all kde related packages including qt to be sure that you won't have compatibility problems. I guess the KDE stuff is pretty interdependant
EDIT: To run only KDE apps but not run the desktop i think you need kde-libs, qt, and i'm not sure if devel. I don't know if kde apps come separate from the packages but i don't think so.