Eric, good job on the copper air lines over pvc lines in your shop. Thanks for making a blog out of this very important subject. I noticed a number of comments relating to piping materials for compressed air. Many years ago I worked for a company that installed service station equipment. We installed air compressors, fuel pumps, and u.g. tanks, high pressure grease and oil pumps. When it came to air piping we always ran schedule 40 black (usually painted later) or galvanized above ground. We ran copper underground or scotch coated steel. I saw the Osha reference to a no go on PVC and I have many more bad stories about pvc than good ones. Most of my experience was commercial grade and inspected by building officials. In consideration of a one or at most two person shops I would still yield to safety first and not use pvc. Cold weather, impacts, degrading of pipe, glue, and fittings, as well as line shock and vibration to name a few. If you must use pvc use schedule 40 pipe and schedule 80 fittings running pvc as high up and out of the way on the wall or ceiling as possible. Then coming down the wall with metal pipe into the work zone.
On your piping Eric I would suggest clamping off the piping to a solid structure wherever you can pull or strain the piping like at a quick coupler. The copper is not as sturdy as metal pipe so I would add a two or three inch galv or brass nipple before the coupler for a clamping point. I agree with adding a drip leg drain where you drop down the wall to a 90. Good looking shop, hope you enjoy for many years.