Yes crank arms should be included within the motor kit. They did for both my M600s and M620. They are Bafang OEM and likely 170 mm in length. Lower to decent quality, but too long for many that will go shorter 155-160 mn to minimize pedal strikes that most emtbs are prone too...even lighter ones like the 820 builds ...just less from what I hear due to slightly lighter motor.
I doubt the stock Bafangs are lightweight. But they are listed as ISIS interface compatible, so lots of aftermarket crank arms that will be much lighter and higher quality are out there to purchase, both carbon and alloy. Which is awesome;
Just Google Bafang m500/600 crank arms and see if a weight is listed...I'm betting they'll be close to the m820 ones.