Seahorses like low flow and are very slow eaters. Fish outcompete them and they will eventually starve if you don't make sure they are getting their fair share at feeding time. I'd only keep them in a seahorse only tank.
You are kind of limited with what you can keep with power compact lighting. Generally, mushrooms need lower level lights and
SPS corals (Acroporas) need T5-
HO lights or even better, Metal halides. The button polyp corals vary in lighting needs - anywhere from med to high. You can adjust the intensity the corals are receiving by their placement (vertically) within the tank. For instance, if you're running T5's with acroporas, you would most likely want them in the middle to upper regions of the tank.
For powerheads - It's better to have varying flows around hard corals, you don't want to have a coral in the direct path of a
powerhead. Tissue damage could result. You can achieve turbulence by having two powerhead flows meeting in the middle of the tank, or bank the flow off the glass to create more of a turbulent instead of a direct flow.
Don't waste your money on the combined power filter/skimmer. Get a stand alone skimmer. You won't regret it. I do like the Aquac line of skimmers. They even have a nano-version now, but I'd still get the Remora model since it's only $30 more than the nano version.
