If a person wishes to stop smoking gradually, how many cigarettes should s/he smoke per day?

Depends. Start with the number your currently smoking and every 2-3 days leave another one off. I would prefer to see you throw them away now as you are not addicted to tobacco leaf but to nicotine. Eliminate all of the pollutants by getting nicotine products and wean off of these. The most successful stoppers are those that throw out all ash trays and triggers to smoke essential oils are very helpful.
See below. This won't work. As you reduce, your smoking behavior changes and you continue to extractas much nicotine and oother harmful chemicals. Use other means.