Thank you for your posting.
To answer your first question, a few extra months of community service is not going to make or break your application. So, if Columbia is your top choice and you are willing to commit if accepted, then I advise applying in the ED round. However, there are clever ways to demonstrate community service without actually having to have an extensive community service dossier.
To answer your second question: Columbia has many more qualified applicants than available spaces so they are not going to admit a person who does not meet their standards just because they applied ED. However, I do recommend visiting the school and/or attending information sessions in order to meet admissions officers, faculty, staff and student. You just never know who you might make a connection with and how this might impact your chances of admissions.
Regardless of which route you take, you are going to have to submit a compelling and competitive application. This requires a significant investment in time, energy and resources.
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