There are a 101 ways to setup a tank, all of them good. I have gone from nothing but a tank and an airline (really complete setup), to a tank with a sump, refugium, protein skimmer, closed loop, auto dosing devices, chiller, HQI's. Kind of the whole gambit.
To know what equipment you need, we would need to know what you want to do.
Is it going to be a seahorse only tank with no other fish or plants? Do you want a planted seahorse tank? Are you looking for more of a reef tank were seahorses will be comfortable in? Do you want all modern and sleek with just a tank, a huge hitch, and seahorses, nothing else?