The point on the company's team is the most salient, I think. If this is your first startup, making sure you're a good fit for them and they're a good fit for you is really important. Consider a couple of the reasons people join startups:
1) To learn. If you join a company with bad founders, poor communication or inexperienced members you can still learn, but there are barriers to learning that are unnecessary.
2) To have a significant stake in something new. If your team does not value you, it's easy to get discouraged and stop caring about the product or to feel marginalized and worker-beeish: If you wanted to build something for someone else, why not just work for a more established company?
3) To build work experience. If you don't fit with the team or the team sucks, it's going to be really hard to put on your resume for your next venture/application.
In short, at an early stage startup, your place on the team can literally make or break the product. If you guys work well together, the product will fail or succeed on it's own merits; if you don't work well together it can doom the company.
Would be interesting to hear about how he stumbled on the position. Startup recruiting just doesn't happen the way corporate recruiting does. Does that mean being up in the bay area (or other startup hub) is crucial to landing a great startup experience? Outside of co-founding your own...
This is a question is sort of a chicken/egg problem. By the time you're ready to be a co-founder you usually are one or have been one before.
It's like being a parent, really: Reading every parenting book on the planet, getting a degree in Child Development and attending lamaze classes won't make you a good parent. Being a good parent will make you a good parent.
By all means strive; but by the time you're ready you'll probably find months or years of being a cofounder behind you.
