It seems that working out the correct point to rotate around is not necessarily as simple as it may sound ...
It requires some precision trial-and-error, that's right. And usually, that point will change when focusing and---with zoom lenses---when zooming, too.
... some say that the nodal point and entry pupil are not one and the same thing ...
That's right. They are two completely different concepts. Contrary to common belief, the one relevant for no-parallax panning is the entry pupil, not one of the nodal points.
... and others even say that they are different depending on whether you mount portrait or landscape
What a strange idea! Of course the camera's orientation (portrait or landscape) won't affect the position of the entry pupil.
... have always found the world of nodal points and panoramas confusing.
That's because nodal points have nothing to do with doing panoramas.
... your input would be much appreciated.
Input from others regarding the exact positions of the entry pupils of particular lenses are mostly useless ... they are hardly more than just starting points for your own gauging of your lenses' entry pupils at various focal lengths and focus settings.
By the way, the identification of the entry pupils' positions has to carried out more accurately when your panorama will include foreground items---the closer the closest item, the more accuracy is required. The farther away your subjects are, the less accuracy is required. If you're shooting landscape panos at infinity without any forground items then you can safely ignore the whole entry pupil issue entirely.
-- Olaf