[cheatbobb]

a) Have a gani script always active, but only show the information if the mouse is in the right position.
b) It hasn't created any lag in my experience, but I haven't had the chance to try with many players at once.
c) Reading variables shouldn't create lag, as they're readily accessible and you don't have to "request" them or anything. Looping through all the players would give you as much lag as a custom chat system would, namely about none. If reading them does actually take a "request" or whatever, then the answer to b) would most likely be none.