Autofocus will probably not be possible with it. Source: https://www.lriese.ch/teleconverter-compatibility-chart-nikon/ The 80-400 becomes a 9-11/160-800mm with the converter. With most DSLRS, autofocus ends after f8.

No, that does not fit. Teleconverters are designed for specific lenses. Nikon TK for Nikon lenses and Sigma teleconverters for Sigma lenses. The F mount, which is actually the same, doesn't help either. The Nikon website will certainly provide information on which lenses the Nikon TK fits.

To be tested, but probably not. But considering the max focal length, I advise you to focus manually. Have a nice day of photography.

The compatibility list can be found under Download. Objects not listed are not mechanically compatible and cannot be mounted. I am not convinced by the product. The photos are sharper without the converter.

Such a teleconverter can make sense for fast lenses. Why should it work for all lenses? If that were the case, there would be people who would mount it on a low-light zoom or a standard zoom and then complain about the image quality. Those who have no use for it simply don't buy it. Nikon F is dead anyway.