Why the question about not giving +1 to spot metering a person's cheek? And how is "middle grey" important for that?

If the spot meter is calibrated correctly (baseline calibration = variation from metered reading as dictated by user testing; or filter factor compensation) it should not need any additional 'throw': spot metering takes skill based on experience; obviously here in this thread so many people have so many variations on what to do, but a bigger problem exists: it is not practical to use the Zone System with small format roll film. It might be approachable with multiple formats of film/backs in e.g. 35mm and MF with a fairly arduous amount of darkroom labour and/or cost and a lot of knowledge. The problem is the brightness range of scenes that vary greatly and if exposures are carried out at different times one brings into question, "what's the point of this?" as you will simply end up with stack upon stack of perplexing, frustrating and nondirectional results. Basics first would be just to spot meter, expose, record notes, then examine the negs then repeat the process until you (not APUG) are happy with the results. There is a lot of latitude in B&W film and I would be inclined to just let the [35mm] camera do the metering for you (if it is a modern era camera with multipattern/evaluative metering, which by design is formulated around the Zone System), with judicious intervention of ad hoc exposure compensation based on actual shooting experience. An all manual camera of course allows you complete freedom to meter the scene intricately and this is what I think you might have (correct me if I'm wrong).

The AA books are a good read, but also very demanding in terms of learning curve. I suggest leaving the Zone System to the larger format where it allows for full creative expression in the darkroom at the print stage.