RE: Carleton visit. This is probably too late for you, but for any others who might be reading this, the best way to get a true feel for Carleton (or many other small LACs) is an overnight visit when classes are in session. Carleton has a long Winter Break (starts before Thanksgiving and ends after New Years). If you visit now, you’ll find a mostly empty campus. Many offices, classrooms, labs, dining halls, facilities and all the dorms are closed or on reduced hours, so you won’t see very much. Even the Arb is mostly barren trees and dead grass this time of year, although there can be an eerie beauty to that. You can imagine yourself being in a Lord of the Rings type movie or something like that.
https://apps.carleton.edu/admissions/visit/plan/calendar/
RE: 1, 2, 3. My situation had some parallels to yours. I had a perfect 800 SAT math score, verbal score in the high 500s, perfect SAT subject scores, and while I can’t remember my ACT, it was fairly good, National Merit Semifinalist. My grades, however, were all over the place — everything from A+s to Ds. I’m not sure what my GPA was, but I think it was in the neighborhood of 3.4 or 3.5 (weighted) in my sophomore year, steadily improving afterwards. Class rank was somewhere in the top fifth, but not top tenth. Even back in my day, these stats were a little on the low side for Carleton. On the other hand, I wrote an essay about one of my extracurricular activities. It really impressed everyone who read it. One of my recommendations was from a teacher in one of my A+ classes and who knew that I had done a very significant amount of independent study in the subject. (The amount of time I devoted to that independent study was one reason for my uneven grades.)
I strongly suspect the combination of my essay and teacher recommendation was what got me in.