Let it also be known that keeping seahorses really aren't for the novice saltwater aquarists, and it should definitely not be in your possession if you are just currently starting a saltwater tank, with no prior experience or handling regarding saltwater aquariums. You can do whatever you like, but it is in your best interest to get accustomed to the whole saltwater game, and how everything works, and experience some of the ups and downs that come along with this hobby before you step up your game to the animals that require more experienced handlers to not only be kept alive, but happy and thriving. Because in a saltwater tank, your main goal is for your tank not to just live, but to thrive.
Also, just something to think about. Starting up this 50G tank will not be cheap. If you plan to have coral, you will need excellent lighting because 50G tanks are pretty deep and have lots of surface area, and lighting is NOT cheap, even for small aquariums. You will also need a great skimmer as well because in a tank that large, proper filtration will be a must. So you definitely can't skimp on filtration for a 50G tank. The link that mfdrookie posted will help you with the rest of the things you need like heaters, ro
, and the likes. But nonetheless, a 50G tank is a great place to start and you're very lucky that you received this tank as most tanks over 40G's are very expensive.
Remember, the only stupid question is the one you don't ask. So if you have any questions, please ask us. It's what we're here for. To help.