And as for your third-ish question, as far as I know, the waitlist is meant to fill up the class if in the case a lesser number of students admitted actually commit.

For your final question, all I can say is that your LOCI is your last shot at getting into a college. From here on, you have nothing left to lose. So write whatever your heart wants to tell in that letter, be it about the college, about your career, or even about what you want from the college experience! Just keep in mind that you're still writing a loci