I don't think the images show evidence of oversharpening, in fact, I wonder have they been sharpened at all - I find scans from the Nikon always benefit from the application of unsharp masking.
The pictures are probably underexposed by at least a stop - given the lighting in these subjects, you would need to allow additional exposure on the main subject at the cost of having the sky somewhat lighter than you might like. Underexposure = enhanced grain. In the case of the Nikon scanners, this is made worse by the fact that the light source is generally considered to be "harsher" than many other scanners
Regarding the Nikon autofocus, it does need an area of detail to function properly. By default it looks at the middle of the image - in these examples I would guess this was a plain area with little detail. Switching to manual mode and moving the focus point to an area with more detail - reg. number, window frame may help.
Colin K. Work, Pixstel