When you write "power bank" does one assume you mean a 5V supply that would normally supply power for a cell phone?
There are a lot of anemic "power banks". The ones about the size of a fat cigar can provide 5V @ 500mA for an hour and a half, barely enough for one motor.
rant on power banks. The specs are usually for the batteries inside them, not @5V. even then, I have never found a power bank to live up to expectations. The best ones provide about 80% of spec mAhr and the useable output current about the same.
My experience with motors is that, because motors are electrically noisy, each should have its own power supply. Putting an appropriate electrolytic capacitor across the motor probably could allow for one supply. But ...
How much power will the motors need? Let's say 1/2 oA per motor. For you other component 100mA and 50mA for the Arduino. So three fat cigars will get you about an hour and a half.
So check the specs of your motors, other component, and Arduino. Size the power bank (using real numbers) for twice what they will use.
I hope the project works out for you.