Hi Jeff,
I (almost) never do portrait. Usually, my subjects do not move, so single-point focus on the back button is my default setting. That same mode will serve you well if your subject is posed and does not move at all. If it does, then, having almost no experience at all at portrait, I found that the easiest for me, on a Z7 II, was to use eye detect. It is a bit cumbersome and slow at first, because you have to fumble with buttons and joystick on the back of the camera, so if you, like I, use the viewfinder to frame and not the back screen, it is not easy. If you use the back screen to frame your shots, the camera is away from your face, making the fumbling easier.
Regardless of how ill at ease you are at the beginning, you soon find that once you’ve nailed the face you’re interested in, the system is very good and does follow that person’s closest eye very accurately. All in all, I would recommend eye detect mode. You may end up with a few misses, but you will also have many hits, which is very important, especially if you work in low light with a fast lens wide open, or almost. You can go to burst mode as well, so as to grab more than just one shot while your shutter release button is down (also helps with eyes half-closed and other such transient problems), and use silent mode as well if you want some discretion to avoid frightening your subject with long photo bursts.
Good luck!
