Saul
Whatever you do, over engineer your main pipe that all the 6mm air lines come from, regardless of what you will be told, 25mm pipe will act like a compressor tank and give even flow all around, the other side of it is, it won't flog you pump out so quickly.
I like 25mm white polly it is easy to work in and you can use garden irrigation 6mm fittings for the airline, thread one end and nob the other, to make a threaded hole use a self tapping screw that is the same thread and size, cut the screw head off and use it in a cordless drill, makes a perfect hole to screw the fitting in to, one more tip, have the compressor pipe higher than the tanks, that way in a power out you don't get syphon back to your pump. OH clear poly glue is AOK as you don't get to the pressures that need the strong glues and the clear wont show up the messy gluing if you are anything like me LOL
I have heard silly things in the past like no using big main pipes because the pump won't work?? It leads to the pump working too hard and shortening its life
I have built lots of shops and fish rooms so any questions fire away. Pump what ever is recommended as you wont be flogging it with that set up
Bob