I plumbed my shop with 1" galvanized pipe. Off of the compressor I have two 1"inline filters and at each drop I have a 1/2" regulator that is off of a tee with a blowdown valve at each also. You do not want to run black pipe as it will corrode inside. Either galvanized or copper or stainless is your best bet. Do not run your header in 1/2" run it in 3/4" or 1" and then do your drops in 1/2". Don't forget to remove that crappy draincock in the bottom of the tank and pipe it out with a proper valve so it is easy to drain your tank after use. This will definately extend the lfe of your system. This is exactly how we install instrument air systems in plants worlwide so I know it works. Oh and yes your CFM will be affected by that 1/2" pipe to some degree at the user.