Without knowing what will be in the rack, it's impossible to know. If it will always have open sides, I wouldn't worry about cooling. If that ceiling vent will usually provide for removing warm air, it won't be a problem- convection will do the job, but not if the side and back panes are in place. If you do enclose it, open the top, use fans and make sure the bottom of the rack has vent panels and the fan can move enough air. Still, it's hard to say without knowing if it will have network gear or a be full of inefficient audio amplifiers.