In YC experience, 2 or 3 co-founders seems to be about perfect.

In the early stage of a startup, hiring senior people is usually a mistake. You just want people that get stuff done.

You think you have this great idea that everyone's going to come join, but that's not how it works.

Remember that you are more likely to die because you execute badly than get crushed by a competitor.

Firing people is one of the worst parts of running a company. Actually in my own experience, I think it is the worst.

The track record for founders that don't already know each other is really bad.

It's better to have no cofounder than to have a bad cofounder, but it's still bad to be a solo founder.