McMaster-Carr #6867K557 for my sprocket on the motors.
Then McMaster-Carr #6295K232 for the gear rack.

For your cable management its called a drag chain or cable carrier. McMaster carries them but they are very expensive. Check ebay and you can find it much cheaper. One good rule I've learned from drag chains so far is get bigger than you think you need.

For example lets say I'm running 4 Cat5 cables with each cable having a 1/4" diameter size. You would assume I only need a drag chain 1/4" tall by 1" wide. I would double what ever you guess is because the cables need plenty of room to flex inside. Also you can run the drag chain from the center of your axis because that will cover the whole axis when it flexes. They do have a bend radius to look at (if you can find it) So in my case I have 4ft of total travel and my drag chain is 3ft long (1ft for the bend)

As for your mill I would recommend staying away from gear and rack as your method of movement. The resistance you get from a router or end mill bit hitting material causes it to push back creating backlash. Look at threaded rod with a backlash coupler on each motor point. Once again McMaster-Carr and ebay will be your best friends. I built a little 7"x7"x7" mill using linear rails, threaded rod and backlash collars and it runs like a champ.