Your sentence is okay but it doesn't meet your requirement of equivalence between the two parts. You could move up "not only" or change the structure slightly. 1. A not only is a good man but also contributes a lot to the community. (both parts now start with a verb) 2. A is not only is a good man but also a great contributor to the community. (Both are subject complements - Mr. Ueda's version) 3. Not only is A a good man but he also contributes a lot to the community. (Both are full clauses)

I am not sure if your sentence works, though I would say "X is not only a good man but also a great contributor to the community.".

It's used to show "in addition to this," that "there's also that thing." It emphasizes the meanings to make them stronger. "It is not only expensive, but also likely to break." "They do not only look good, but also taste great!"

Both parts should be both positive or both negative. Example: “He is not only ugly but also fat.” “He is not only handsome but also strong.” You wouldn’t say “He is not only ugly but also strong.”