Dear deckardbr:
I think your concerns are valid as Columbia is a highly competitive program. You will need to explain your career path and why the MBA makes sense in this path (both as the next step and the timing). Likewise, how does what you have done in the past lead you to what you want to do post-mba? As for extra-curriculars, you do have some things you can talk about, but if there is an opportunity to get involved in an activity you are really interested in, then do it now so you will have a good amount of time prior to the application deadline.
It is important to visit the program and get to know the admissions staff. If you can't get to the campus, then take advantage of every opportunity to meet with someone in person that you can. Lastly, you need a strong GMAT score and a strong application submitted in the first round.
Best of luck to you!
Lisa