I agree! You def still have a shot at USC! A 169 is past their 75 percentile, you just have to make sure all your essays, recommendation letters and resume are spot on.
Congratulations on that huge improvement! I'm so excited for you :)
Yes, I absolutely would. You said yourself they are a top consideration of yours and I think it would help immensely for you to express that in a separate addenda. And yes, it is acceptable to add it on as a supplemental addenda!