Hopefully this is not too stupid a question...

A full KDE desktop is really too much for any of my computers, but I still like using KDE applications. Some of them might require PIM stuff though. What's the best way to make sure that akonadi, nepomuk, and other necessary services all start along with my choice of minimal WM?

KDE PIM applications will automatically start Akonadi - which will start Nepomuk (I think) as needed.

If Nepomuk is not automatically started, then running "nepomukserver &" in a terminal application (such as Konsole) prior to starting a KDE PIM application should be sufficient.