You can't be focussed without really great communication

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

... for the top twenty most valuable YC companies, all of them have at least two founders.

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

More important than starting any startup, is getting to know a lot of potential co-founders.

You can't be focussed without really great communication

In general though, if you look at the track record of pivots, they don't become big companies.