As I understand it, if you chose to go in one direction, lets say 70:30 run
***, the run is more likely to succeed, but the pass play suffers. Same goes with the defense, so I suppose the best thing would be to use a 50:50 or 55:45 ratio, unless you really want to be a one dimensional team.
Aggressiveness on defense seems to determine, how many big plays you give up in order to stop the opponent in short yardage situations. The more aggressive the more you will force a 3 and out, but you are vulnerable to a big play.
On the offensive side of the ball, I have no idea.