This is similar to the system I plan for my garage and a big expansion on the same style my dad has in his garage. Seems very standard way to add air to the garage. My dad has a loop, I was planning to save on pipe and do an H. I am a bit surprised he is using steel - it seems very yesterday to use steel - I have copper and so does my dad. Copper may also be a bit old in the tooth but it does not have the rusting problem of pipes at all and looks great.
My dad has the same style of drops with going the way up and then down. I am thinking of just straight drops - simpler and easier to install. Also easier for air flow - I am unsure as to whatever the U actually help that much with water.
Main line would be 3/4 inch pipe and most drops would be 1/2. Overkill but not as much as 1" steel pipe.
The 1/2" is good enough for about 30 cfm flow even to the far corner of the shop already. Can easily handle bursts of 50 cfm. Main choke point would be the end air cable and tiny fitting connecting hose to system and hose to tool not the pipe.
For 1" steel pipe your limits are almost endless - it can handle easily 100 cfm or even more continuous over 200 ft.