1 day of research is nowhere near enough, no matter what your reserching. That tank is too small for a pair of seahorses, just because some people have gone as small as 2 gallons for a seahorse tank dose'nt mean it's big eough for them. Do you know what cycling is? you need to research that. Do you have a site in your favourites that deals with hitchhikers on live rock? that will come in handy. Do you know what kind of substrate your going to use?plain sand won't serve you well there. do you know what test kits to buy? You absolutely need to know this. What salt mix do you plan on using? this is'nt essential but something you should have planned out. You also say you want to get a sea fan or some sea grass. do you know what kind of ight you plan o using for your tank? most likely the lighting you have on that tank is an incandesant and will only give you loads of algae problems? do you know if your tap water is good enough or are you using RO or DI water?
these are all questions you should have answered if your ready to set up your tank.