are we playing the same game?
i'll help ya with the first question and let others do the others.
have you tried talking to Z'ant? he tells you all about the assassin.
and for your missing teammate, you were given some dead on clues the moment you came out of your coma. blue flowers only grow in one place. at croc's. so by going there, and talking to the *ahem* creep, you find out right quick what happened to your teammate.
also, as far as i can tell in this game, your opponents are scaled against your level. so, by racing thru at level 17, you will be fighting, what? level 15-25 or so? something pretty close to that. it's when you hit personal levels around 25 or 30 that you start getting into the bad boys.
V***V