Re “I just was worried that compared to a lot of students that have massive lists of ECs that his would look very narrow.”- we had a few college info sessions say they don’t really pay much regard to people who suddenly sign up for a whole bunch of things in junior year as it’s obvious it’s just being done for the college applications. They’d rather see fewer ECs with longer and deeper commitment. So again - your son should be fine on this front. Good luck.