I've been doing start-ups for about 3 years now
Holy shit, how many start-ups is he talking about here?? He must really fucking suck at it, otherwise he'd be doing "a startup" for 3 years.
NoSQL is a completely braindead idea for a start-up. NoSQL's only advantages are scalability. A single SQL server on commodity hardware can scale to thousands of simultaneous users for a typical web app. If you have more users than that, then you aren't a start-up anymore, and that is the point at which you should migrate to NoSQL (if at all).