Ask a professional photographer to have a look. What processes did the following pictures go through in the later period?

These three pictures are basically not late.

If we want to say later, it is only in color matching and correction. (But this is also related to the camera; The lens has something to do with it. )

Is it possible for an entry-level SLR like Nikon D3 100 to shoot this effect?

The main effect lies in the early shooting, which depends on your lens. If your lens uses a set of digital cameras, it will not produce such effects, such as the small depth of field in the second picture, the halo and dotted lines in the first picture. Then we need to do some halo and blur processing later.