Wiring and grounding stepper motors
It probably won't make a difference. If you google "wire resistance" you can find tables that deal with your setup. Basically, 18ga wire has a resistance of 6 ohms / 1000 ft. 6 feet will be just about .04 ohms. Your motors are 1 A. So for B) the voltage drop to the first motor will be .08 volts, and to the second, .16 volts. For A) the numbers are .16 volts and .24 volts. If you're using an H-bridge with current control (rather than switching 5 volts), this will make no difference at all. If you're switching 5 volts, it's still a small effect.
Sure, go ahead. It won't matter, but it might make you feel better about the possibility of pickup. Ground the bare wire at the controller end and not at the motor.