f16 will always be less sharp than f8, independent of type of lens, because of the physical effect of diffraction.
Possibly, but product photographers shoot at f16,18,20 all the time.
The product has to be in focus front to back and with possibly hundreds of shots a day you don't have the time or money to take multiple images of each and then combine them.
If you use high quality lenses that go to f32 or f45 it's no problem.