You need to decide on the diffusers so you know what to get for barbs. My setup above runs to 10" diffusers from Hydrofarm - think those diffusers use 5/16" barbs. Or at least that's what I used for line I believe.
I run valves to compesate for the diffusers plugging up at different rates and to move the boil, have built without and had to add them to have the ability to "tune" it.
Is this just when running multiple moving beds or if you run one with too much air will you have a problem? Short of the media launching out do you need to dial it back at all or is the tuning you're talking about solely due to them plugging at different rates, aka dialing them all back to an extent and then dialing them forward as they plug?