"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
There can be a tie. In this case, both winners come back for the next game. In one instance many years ago, there was a 3-way tie.
no i watch it everyday and not one person won an amount that was NOT allowed because of some "limit"
no as long as you win you continue to come back
no
Did not even see the name as a Contestant on Jeopardy at the Jeopardy Archive related link
5
$100,000. http://en.wikipedia.org/wiki/Jeopardy!_College_Championship
So someone can win
no only the winner
no
You have to win 100 consecutive times.
You win 1000 dollars if you are third place and 2000 if you are second place because someone had less than $0.
5
77,000 in non tournament play
21321 times
4 times