I'm pretending to work, so I have to core dump this quick:
The greater the temperature differential between the rack and the room, the less fans are needed.
Generally wider racks are better for the chimney effect. One of the reasons a wide rack runs better than a thin one, or a shelf setup, is because of the 'chimneys' on both sides of the rack. If you do have to use a closed wood shelf system, have the outsides of the shelves cut out along the interior walls.
The other thing that I see a lot which is a bad idea is installing vented panels between front intake equipment. This causes the air to come out the back and have a path of recirculating to the front. Shelf setups are very bad with this, because their backs are blocked and the only way for the hot air to escape is through the front of the shelf, leaving it to get recirculated into the equipment.
Rear intake equipment (front exhaust) should be separated from front intake equipment with a panel.
On shelves, often times a blower is a better selection than a fan, because blowers are capable of 'sucking' at higher static pressures like would be developed in a wood shelf with gear that is front to back cooled.
Also, always run a bit more intake fans than exhaust fans, because it keeps the pressure positive, which makes dust tend to move away from your equipment rather than into it.
Keep intakes away from exhaust.
Now back to work for me.