Welcome to AA!
You might want to get something easier to start out in saltwater. Seahorses are pretty delicate and like Doug said, check if they are eating before you buy any. Dwarf seahorses also require live food daily so make sure you can provide that. You will want live rock and macroalgae for the horses to hitch to. I think it's possible to go reef as well if you really want to. They mostly need branching structures to wrap their tails around. Here is a great guide to keeping dwarf seahorses: The Care of Dwarf Seahorses - Seahorse.org
I wanted seahorses as well starting out in saltwater but they have a lot of requirements and I personally don't have the time and resources to keep them happy. If you feel you can provide well for them, definitely go for it!