There are zoom lenses that have macro capability, but not usually the quality of a lens made specifically for this purpose. No, the sigma macro lens changes length with the distance to the subject in order to focus. As I recall, the closer you want to be the longer the lens becomes - but it will stay at a fixed focal length - like 105mm.
Used lenses that are properly taken care of are just as good as new. Some are even rarely used to the point that they look new. Many people try them and put them away and hardly (if ever) use them again!
About the light ring - I can see where it would be useful, but if the subject is not moving and you get a good tripod you can usually do with natural light for most subjects. Another concept that would be good for lighting would be a light "box". Check out this site - I'm considering this as a good photo tool(s) -
Flower photography tips - how to photograph flowers