Can I operate a well pump with no pressure tank by using the breaker as a switch?
Not really.

You can do that if you only turn on the pump when you're consuming water. You don't want the pump running if no water is moving. You'll wear it out. 

The point of a pressure switch is to prevent just that, and the point of the pressure tank is to reduce the frequency of pump startups (along with stabilizing pressure during usage).