I wouldn't worry about shorter or custom-length cables.
having a little room to play with is good if you need to remove the equipment but still have it plugged in (repair, etc)
I have two racks:
one with the mp3 player and mixer. the back cover slips into a slot at the bottom and attaches with a latch at the top. When I use it, I latch the top and let the bottom hang free, and pull my connecting cable out the back and around the sides of the rack, so they hang on MY side of the DJ table.
the second rack is for my amp and EQ. this one has a back cover that never comes off. I have attached a connector panel for ac, audio in, and speaker out plugs...which again is on MY side of the table, out of view from the crowd.
If you find a way to pull your cables thru YOUR side of that rack, rather than out the back, you can simply leave the back rack cover on during the event.