1) is obvious. Figure out commuting distance/gas mileage = amount of gas burned.
2) Might be hard to prove outright, but research shows that people often feel better after exercise if they go at it pretty hard due to endorphins or other feel-good chemicals being released. Also, biking probably helps wake people up better than driving. Additionally, if you live in an area with crappy traffic you could argue that biking alleviates driving-related stress. EDIT: You do, I just saw the Orange County location. So there you go.
3) I don't know if those precise statistics exist, but you can definitely show that exercise leads to better health and higher quality of life. The difference is greatest for older people but everyone benefits from exercise. From a purely anecdotal perspective, I've always noticed that I get sick less when I'm exercising regularly, and less severly, although I wouldn't claim a definitive mechanism there.

Here is a link to exercise==feeling better
http://news.bbc.co.uk/1/hi/health/1565230.stm

And one for general health benefits from Mayo clinic, including health and mood
http://www.mayoclinic.com/health/chronic-pain/AR00017