my neck was in the 18 inch range. I stopped training my neck completely and haven't had a problem since. But now I'm a pencil neck, just measured it at 16 inches on the nose. I was going to buy one of those helmets once, glad I didn't.
I guess a bigger neck can look cool up to a point. One little young natural youtuber claimed the harness will improve facial aesthetics too which I don't know anything about. Speaking of facial aesthetics, I had reason to ask my dentist about training the jaw muscles and she was immediately dismissive, no, no, no, don't do it, even exessive gum chewing was dangerous. I was a little pissed because I wanted to know why but she wasn't about to discuss it, just said maybe in specific cases where your jaw gets no stimulation and then you also had to train the opening motion.
17 inches be it muscle or fat iirc above it likely you will have some degree of apnoea
Ah ok, so already at that point, that's not exactly huge.
Regarding the CPAP, I saw bb forum posters complaining about how the machine with straps that crunches up your face causes folds making you look old.