I just published an article in Forbes on social enterprise: http://www.forbes.com/sites/85broads/2014/06/18/social-entrepreneurship-is-it-right-for-your-company/
I don't believe a social enterprise should be a non-profit. It should be for profit with a mission.
In my article, I touch on the funding issue. That has been a concern for me as well. My startup isn't a B-corp now, but we are considering it. The whole concept is somewhat new, but companies like Ben and Jerries and Newman's Own or Terra Cycle have so far been successful with the concept no matter how they are structured.