The relays are de-glitched on the relay board. I like that your -12V lines are all returned to the - lead of the power supply (single point ground, motor current not flowing anywhere in the Arduino PCB); that makes ground-loops less likely.
Try it.
If you get noise in the AD input from the positition pot, put a 10uF capacitor, + to the AD input, - to Uno local GND. A 0.01uF disk ceramic capacitor between the red-black motor leads (close to the motor as possible) might help...