Theo,
Can I just put the compressor in barn and run say a 1 inch PVC line 350ft to the waters edge and then split it off at a manifold to 2 or 3 diffuser set ups on 1/2 or 5/8 weighted airline.
Yes. I run air a little over 600 feet to one pond (from a shed at the other pond) through 1" black plastic water line, and then select the deep water (Summer) or shallow water (Winter) outlet with 1" ball valves in a manifold clearly assembled by the Son/Grandson of plumbers. I switch from the 1" line to weighted airlines just inside the pond's shoreline.
I would ensure that the location in the barn was dust/dirt/vermin free (say with a sealed cabinet with filtered air input, if necessary).
Also how loud is a 1/2hp rocking piston compressor compared to say a lg garage air compressor?
I believe my aeration compressor is quieter than my tire compressor. (A cabinet with sound insulation would help that.)