As for focus tuning a new camera, Nikon bulletin 15896 says,
The "AF Fine Tune" feature allows users to make focus adjustments to compensate for minor differences in their particular lens and camera combination. In general it is not recommended to adjust the AF Fine Tune unless you are having a specific focus issue, as unneeded adjustments can decrease the overall focus quality of the camera.
There are many ways to test and set the AF Fine Tune but one effective way is to reproduce a "real life" situation where a problem is suspected. For instance, if you feel that the focus is incorrect when shooting close-up subjects, you should reproduce that type of shot.
Place a subject with depth (a ruler works well) into the scene and focus on a pre-defined spot. Choose "AF-S" focus mode, make sure that the focus point is on a part of the subject that can be easily focused upon; see the camera manual for tips on autofocus point selection. Take a photo and review the results on the computer.
If some part of the photo other than the selected focus point is sharper than the focus point use the AF Fine Tune adjustment. Adding a "+" correction will move the focused point away from the camera and would be used in a "front focus" situation. A "-" adjustment moves the focus closer to the camera and would be used if the test photo showed the focus behind the selected point.
The "±20" range is an arbitrary scale and does not represent any actual distance. Trial and error will be needed to determine the best setting.
Up to 20 different lens or lens converter adjustments may be saved. Zoom lenses should be tested at the middle of their focal length range unless a specific error is seen at one particular setting or the lens is always used at particular zoom setting,
If the AF Fine Tune does not increase the sharpness it could indicate a more serious problem, and the lens and camera body should be sent to Nikon Service for evaluation.
I would summit that any new camera shouldn't have gross focusing problems with reasonably late model lenses.
Other forums are suggesting that there are some D7Ks that have some focusing problems.
Ratcheting a lens to +/- 20 units to get it to focus seems out of whack.