The current consumption of the coils is 35 mA per coil (so 140 mA total). You can power your project from a PC or an external 5V supply (on the 5V pin). Do not try to power from the external supply and have USB power (from PC) connected at the same time.
I'm not sure about transient currents.
What do you want to control? Depending on answer, you can consider a 'pure' electronic solution.