The exterior is 3/4" plywood with an oak veneer. The middle shelf is fixed and is also made of plywood with oak veneer. We also put an oak veneer on the front of the fixed shelf so it does not look like plywood when everything is installed. The sides are pocket jointed for strength and everything fixed is glued as well.
The other 4 shelves are removeable so I can have some flexibility. Scott had a jig so that we could drill holes for push-in dowls. The removeable shelves are made out of 3/4" MDF with an oak veneer on both sides and we also put some oak veneer on the front edge of those shelves as well.
As far as the install... I just set it up in there to make sure if fit. When I do install, I will shim it into place, then counter-sink some screws in. Since I'll have 150-200lbs of equipment (+ the weight of the rack), I will put in some support legs for the rear. I will also make a removeable panel in the rear to seal up the rack, however, I will be installing a bunch of cooling fans to suck the air out so I never have to worry about heat.
Toward the back of the shelves on both sides, I will use a holes saw all the way through to allow clean routing of all the wires. I will have the power come out on the bottom and everything else on the top since placement of all my connects pans out that way.
Here is my rough paint sketch....