This 28-300 really does replace every other wide, normal, tele, macro and zoom.
The Nikon 28-300mm VR is sharp at all settings.
Your equipment DOES NOT affect the quality of your image.
Photos that are sharp all over are usually amateur attempts, which glaringly show too much detail for many unrelated, confusing and distracting elements.
Focus scales are a throwback to the 1930s when cameras were focused by guessing or measuring the distance, and then setting it on the scale. This went out of style in by the 1950s, when the scale served as a computer for landscape photographers.
I like the plastic mount. It slides on and off my cameras much more smoothly and easily than my metal-mount lenses.
On my Nikons, I use Professional mode, the "P" setting, so the flash only goes on or off as I tell it. Other modes work, too, but you might have the camera forcing the flash on or off by itself, or have the camera run out of shutter and aperture options. In Pro (P) mode, the camera does whatever it needs to to give the best shot it can.
Most Nikons since the 1990s have done this more or less perfectly, and today's DSLRs are even better.