The Death Note is a book which will never run out of pages, anything like fire or acid will burn the pages. It is mysterious of how the power of the book operates the pages but it's clear that it has the ability on murdering those who names are written down. In 40 seconds, one person will have 2 posts to die if they are in a topic separate from the one where they die or a person will die in 1 post if they are in the same topic where there name is written down. Blood is acceptable for being written down, but saliva will not be acceptable.
There are only 2 kira's available. Ownership and that information is explained
here.
Those who touch a piece of the death note or the whole book will be able to see the Shinigami which owns it. Shinigami can naturally see each other.