Take this with a grain of salt since I’m an incoming freshman, but I chose Caltech over several of the schools on your sons list for computer science and didn’t feel it was significantly ''more intense" than schools like Harvey Mudd and UChicago. Caltech has a unique quirky culture that fits students that may not have been considered normal in high school. There are definitely opportunities to do things outside of STEM (I plan on double majoring in a humanity and playing a sport). My friend is a physics major at Vanderbilt and enjoys how small and friendly the environment is (I don’t know much about it though since I didn’t apply). You seem to have a lot of safety schools. You should be able to cut at least half of those (I regret falling into the trap of wasting money applying to too many safeties this year).