The motors are produced by:
CHANGZHOU CHUANGWEI MOTOR ELECT APP


I can't find much info on the net, but they may be similar to the 150 sub-type which is rated at 1.5A.

As to the resistor, the current through the stepper coil also goes through a measring resistor and thus generates a voltage proportional to the current. This voltage is compared to what you set with the pot and defines the cutoff current. There are boards out there that use 100 milliOhms and also 200 milliOhms. You will need to verify which one is on your boards. The datasheet of the driver chip also provides more info on this.