It all depends on what you intend to use the "air supply" for?
Most economical is 1" galv pipe...but if the end use is as a spray booth supply...save yourself a huge headache and put another compressor out there....
When plumbing air lines you MUST include drop points with drain valves in each vertical drop line....below the outlet nipple....
Dryers are nice...keeps moisture out of your air tools...(and paint!)....
In long runs, I try and install a ballast tank to provide more air supply load balancing...an old compressor tank works well....
Hope this helps...
