Hello,
First, to answer your questions: assuming that the professional level of work is comparable to more conventional MBA applicants, having an unconventional background is can be a plus but also presents special burdens. Adcoms look for diversity, including industry/function, so if you bring an unusual but relevant perspective to the table, it’s a plus. That said, you have to show (a) what’s unique and special about it through your essays, and (b) strong and credible reasons for pursuing a business degree and related career. So it’s both opportunity and challenge – it you take the opportunity and run with it, your different professional background is a plus. Also, keep in mind that adcoms to top programs want to see outstanding work performance and track record, whatever your employment is.
Given your type of education, I don’t see much need to retake the GMAT to improve the quant score – unless you have poor grades in quant courses. Then you should definitely improve it. Also, bear in mind that that GPA is low. I think this will be a problem for some of your target schools.
The European programs you mention tend to have low representation from US applicants, so actually if you do great applications I believe you are a strong applicant to the European programs (including Insead, which would be the biggest reach among them, but still a reasonable reach in my view). I believe that the GPA will make Stanford out of
reach, and Wharton and Columbia would be fairly high reaches but still in reasonable range, assuming (a) a great application (b) outstanding track record at work and (c) good quant grades.