"If two or three contestants tie for first place, they are declared co-champions; each keeps his or her winnings and comes back on the following episode. Three contestants have each finished two consecutive games as co-champions" see related link
Did not even see the name as a Contestant on Jeopardy at the Jeopardy Archive related link
5
You have to win 100 consecutive times.
So someone can win
$100,000. http://en.wikipedia.org/wiki/Jeopardy!_College_Championship
no only the winner
no
You win 1000 dollars if you are third place and 2000 if you are second place because someone had less than $0.
5
2 times
21321 times
4 times