I've never kept seahorses, but I have done a fair amount of research. That is my biggest advice to you. Do a lot of research before you decided to setup a seahorse tank. They are rather "special needs." They need a setup that is fairly different from a normal fish tank. Also, there are fish that can be kept with them, but the choices are limited. Seahorses are methodical eaters, so any active fish will always out-compete your horses, and the horses will starve to death. So, you need to get fish that are fairly passive and totally none aggressive. The fish needs to either also be methodical in eating (such as mandarins) or eat a different kind of food than the seahorses. As to the types of seahorses, I'll leave that to people who have had experience with them.