Admissions Advice (D in Calc)

OK, so here's my deal. I was planning on attending Duke law school, but I've realized that my interests are much more in business. I studied Econ and English at a top 5 public undergrad, got a 172 on the LSAT but do not have a GMAT. I have 3 years work experience already and plan on getting at least one more year before applying.

Here is my worry. I had a 3.3 in my Econ courses and a B+ in my one accounting class, but, unfortunately, I decided to take Calc 2 after not having taken a math class since AP Cal three years before (I got a 5 and was feeling cocky). I was taking 18 hours of courses that semester and meant the class to be audited, as I was taking it Pass/D/Fail, but I was .1 away from getting the Pass, and instead got the D. If I get over a 700 on the GMAT, can I get into a top business school, or will that D be a barrier?

My work experience is in helping manage my family's business, which has almost 300 employees. It is not sexy or rigorously analytical like consulting. Is it still considered OK work experience?

I'm asking all this now because I'd rather go to Duke, a top law school, than get an MBA from a mediocre school. Given my type of work experience, my 3.5 GPA (which includes a D in my one real math class and 3.3 in my econ major and one accounting class), will I be able to get into a top MBA program? What GMAT will I need to get in?

These are the schools I'm particularly interested in: Harvard (obviously no chance here), Penn, Northwestern, Berkeley, Columbia, NYU, Yale, Duke, UVA, Michigan, Texas, UNC

Thanks so much for any advice you can offer.