1. I agree, it’s definitely the nicotine, which is absorbed by the mouth. I imagine it’s similar to the mechanism in which sub-lingual medications are absorbed into the blood stream.
2. Cigars with more nicotine are more likely to cause people to get sick.
3. I’m not sure, but it might have to do with sugar content in the blood and the way it’s processed by the body.
4. See Psychoactive effects in this link:
http://en.wikipedia.org/wiki/Nicotine
5. Yes, your tolerance to nicotine will increase.