Thanks to Theo, Bill and Cary for your input.

I finished the install. From the pump I ran 325' of 3/4" then 3' of 1" to first valve, 60' to second, then 60' to last one. From each valve I ran 1/2" PVC or poly to the diffusers. My first diffuser puts out the most air and declines as it moves down the line. My diffusers are DIY so it's tough to say how much cfm each is putting out. The guage at the end of the line shows 3 psi with all valves open and 5 psi with the first one half closed. The guage at the pump shows 10 psi. I also added a fourth diffuser to a small pond about 30' from the pump.

I don't know what these numbers mean so my fine-tuning will have to be done by sight. First impression is there seems to be some good action, especially from the first diffuser.

Should the most powerful diffuser be in the deepest (8') or shallowest (4') part of the pond?

Thank you again for your assistance.