hmm i like the idea to show only the main message without any numbers; they can be shown in some match stats or sth like that
its not a good idea to base assist on dmg. keep it simple. I mean less is more, up to 100 possible points (bf3 system) is way too much you get too much exp for not even doing a kill. Remember only if a friend helps you, otherwise you will never get this assist bonus because he probably wont die, and will have full health soon!