Okay, so I personally only have a filter and a skimmer on my 56 gallon FOWLR. I don't think you really have a need for airlines and pumps. The filter and skimmer will move your oxygenated water around enough that it should be fine, unless you want high flow, which I don't think you do if you are going to have seahorses in the tank.
I could be wrong on this, and someone correct me if I am, but that is my experience.
Plus, just FYI, in my first saltwater tank, I had an oscellaris clown and a yellow watchman goby in with a seahorse. I can't remember what kind, it was a while ago, but so long as I paid careful attention at feeding time, everyone got along great. I taught my seahorse to eat in one corner, so she would go there at feeding time and wait for me. Sadly, we had a power failure, and everyone died while I wasn't home. But the point is, I made a mixed species tank work, it just takes a little more work and observation.