Gast makes very good pumps and the 3/4 horse should be plenty for your needs. There are other good pumps out there, but I am biased to the Gast Pumps merely because that is what I have.
Look at esshup's web site...
https://shop.hoosierpondpros.com/Aeration_c3.htmand you will find good price points for the 5/8" ID sinking air line and the single vertex diffusers. It's where I bought my line and diffusers. He also has the PondLyfe systems and he may be able to recommend one of those...I'll leave that to his expertise.
The Gast 1023 should be able to run 5 to 9 diffusers nicely. My opinion would be to plan on 7 to 8 with the 1023 (maybe 9 depending). The 1023 is probably overkill, but that is my style at times (I like the extra diffusers for surface conditioning...my pond gets pretty scummy at the surface) . You could consider buying the Gast 0823. It's a bit smaller pump with the same HP (I think), less money and would run 4 to 7 diffusers. Now, if the budget gets tight after adding up all the costs...we can look at the Gast 0523, but this pump might be too small depending on what gets aerated and how deep you go with the diffusers. We'll just wait and see where your budget takes you.
