>2 questions: first, is nicotine inherently harmful? Second, a light smoker is considered someone who smokes less than 10 per day, is there research on people who smoke even less than this, e.g. "socially?"

Copying part of our response above, there is little and inconsistent evidence for long-term harm from low doses of nicotine in adults. Nicotine - including nicotine from gum - can be harmful for the developing brain, which includes young and pregnant people. For your second question, yes there has been research focused on light, intermittent smokers, sometimes called ”chippers” in our field. Check out some of the research by Saul Shiffman.