1. No
2. 20-30 leaves for a quid chew. Smoke bowl after bowl until you're high.
3. Smoking you inhale smoke, and chewing you just chew on the leaves. (buh-dum-bum-tcchhhh) No, but smoking is quicker to come on, and chewing lasts longer and is less intense.
4. Don't smoke plain leaf. It's a waste of lungs. But to each their own.

Hope that helps. Also check out DickJustice's faq in Other Psychotropics, sagewisdom, and erowid for salvia advice. It's not really necessary though if you aren't doing extract, but still recommended.