Because it's possible to get only 500mA trough USB, I think I'll have to use an external voltage. I have some questions.
What would be the voltage then if using the 9V battery and the Vin-pin as an output with servos? What about the total current?
Here it says (link below) that voltage from the external source is regulated to be 5 V. If that's the case, is it impossible to get more than 5 V from Vin when connecting Arduino to e.g. 9 V battery?
You mean 9v to the barell jack, right?
I am recommending to use an extra branch for servos, directly from battery like in "High power consumption 5 V circuit plan" (ttps://www.open-electronics.org/the-power-of-arduino-this-unknown/).
The link is corrected. It is same as you have sent.9V is too much for these servos. They wrote 4.8-6.6V. You will need the regulator. I will go to some switching regulator instead of the 78xx from schematics.