Will I need external power? How to calculate it?

Rookie2:
My doubts are, how to know if the USB is able to provide enough power for my current setup?

You need to know in advance what the voltage and current requirements are for anything you connect to the Arduino, and ensure it is compatible with what you're connecting it to. While you are unlikely to damage the USB itself, it is very easy to damage the Arduino output pins by connecting something that draws too much current from it.