The Ivy League schools, and other highly ranked schools, are definitely not a good fit for every strong student. It also is hard to fully determine fit, or to fully determine how a student will react to any particular environment, until they get there. Transferring out of an Ivy League school seems to me like something that would certainly be a good idea for some students, and would probably be a good idea for more students than actually do so.
I am wondering about a few things. One is what sort of school would be a good fit for your son. Would a smaller school such as liberal arts college be a better fit or would a larger school be better? Would somewhere that was a bit less overtly competitive be a better fit? The other thing that I wonder about is budget: Do you have any restrictions?
Reading “Ivy League” and “rural town” makes me think of Dartmouth College. This in turn makes me think that the highest ranked LACs might not be much of a difference.
If he had 10 credits from AP plus summer courses, plus 9 more from this semester, then he is still ahead of schedule. I would not worry about taking a course over the winter session unless he wants to.
Figuring out what would be a good fit sounds to me like it is the first priority.