I am organising a multiplayer event where each player has a rating (new player is assigned a rating of 1500) ..I want to have a good formula for calculating the new ratings after a competition..I searched the net and found the Elo rating system.This is what I have worked out thus far from the internet resources..:

From The ELo formula let P(B,A[i]) refer to the probablity that B defeats A[i] for all i.
Then total[B]=summation of all P(B,A[i]) for all i's 
Let n=number of participants..
Then Expected Rank[B]=n-total[B]
new rating=old rating+ k* (ExpectedRank[B] - ActualRank[B])

Now the issues:

1)I want to know what value of k should be employed .

2)I want to have a regualrity factor also so that a player who is consistently performing well and if some day performs badly his rating does not go too down .ie.ratings dont change drastically on good /bad performance in one match..

3)If this is not the best method to calclate ratigs in a multiplayer competition then which one should be used??Please give details , formulas also

Please help me out .Statistics is not my subject yet I need to get this thing done to complete my project