@fretfulmother - Your son sounds a bit like mine, who was a strong STEM student but whose interests went well beyond the sciences, for example having enjoyed all the history APs in HS. When he applied to Princeton he listed his possible majors as physics and philosophy; ultimately, he believes the topics are inexorably interwoven.
One attribute of Princeton that hasn’t been mentioned is the writing seminar which is required for all freshmen. I thought DS was a very good writer coming out of HS, but the writing seminar was definitely beneficial for him.
As for the odd winter break schedule, my son liked it that way. He’d come home for a relaxing holiday with a little light studying knowing he’d go deep into finals prep during “reading period”.