Johnny, I agree.
Baer, I didn't receive any specific feedback about taking courses, I just gathered information on my own. Your situation is different than mine though. Your GPA is within the middle 80% range for your target schools, while mine was below. Also, I went to a good and very competitive undergrad (UCLA), but I was an English major which isn't known for being particularly difficult (it was known for good looking girls though

). Finally, I hadn't taken a math course since high school and I knew schools would be concerned about my ability to handle the work.
I do recall one thing that Linda the adcom from Columbia said in an online chat. She said that a single course didn't simulate the intensity of a business school load, so that might not help that much; that's why I took 4 all at once while still running my business. If you're going to apply to Columbia, I highly recommend applying in the early round.