Don’t get too excited about Columbia’s 3+2 program. There are strict GPA requirements for transfer admission to Columbia as the “2” school. It also entails an extra year of costs, and Columbia does not promise as good financial aid for 3+2 transfers as it does for frosh and normal transfers. See http://undergrad.admissions.columbia.edu/apply/combined-plan
In general, few 3+2 intending frosh eventually transfer to the “2” school.