Audio Rack Construction

Happy New Year All!

I'm planning a rack with three wood (maple) shelves using threaded rod as the supports. This will be something similar to Salamander racks. Besides, the metal washers and nuts, I'm going to be using some type of isolation washer that will contact the top and bottom of each shelf.
So...shelf, isoloation washer, metal washer, and then nut.

Questions: 1. When passing the threaded rod through each shelf, should the holes in the shelves not allow the threaded rod to touch, so the only thing touching the shelves are the isolation washers? 2. Besides neoprene, what's a good material for the isolation washers? 3. After leveling each shelf during assembly, I'm planning to add aluminum tubing over the threaded rod and nuts between each shelf for a cleaner look. This would mean that the top and bottom ends of the aluminum tubing would also contact the shelves. Should I avoid this, or additionally add some isolation material between the ends of the tubes and the shelves?