The single word that matters most I think to keep the company productive as it grows is alignment.

AirBnB spent 5 months interviewing their first employee, before they hired someone and in their first year, they only hired 2 people.

You also want people who are maniacally determined and that is slightly different than having a risk tolerant attitude.

There's no way I know, to get through the pain of a startup without belief that the mission really matters.

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

Ideas by themselves are not worth anything, only executing well is what creates value.

You really want to know your cofounders for a while, ideally years.