As you’ve already touched on, company culture is everything at small companies. If you fit in well, you’ll love it. If you don’t, you’ll hate it. I would ask to talk to other people in the company besides the CEO and talk to them about what working there is like and what kind of person would fit in well. If the CEO (I’m assuming that is who you are interviewing with) balks at the Idea, that right there tells you something.