How to calculate the needed voltage and current to supply for Arduino
Voltage is simple - a device has a requirement and that is what you have to provide. In the case of the servos that is a range of voltages that it can use. So 5V is a good voltage.  The Arduino can take 5V if you feed it in to the 5V pin or the USB port, or 7-12V if you feed it in to the barrel jack.

The current you cannot calculate. You haven't provided enough information. The calculation, when you have the information, is quite simple: for all the devices on the same power supply add the currents requirements together. The supply has to be able to provide at least that amount of current.