The best rock will be large and light. This would indicate alot of holes in the rock and thus be able to hold more bacteria. I have some fiji rock and it seems alright. Live rock will cost you quite a bit of money, so I would suggest a combo of dry live rock (much cheaper) and live rock.
Youll need to consider what you plan on having in the tank aside from the seahorses when considering lighting. If you have the money, id go with a nice T-5 setup since youll crave corals down the road.
Get a koralia powerhead or two. They are nice!
Make sure to ask lots of questions on this site before adding live stock! Youll be very happy you did! For instance, youll be sad to know that the live sand you bought, which no doubt cost you some $$$, is waste. Its likely not alive, and if it is, it probably has a lot of junk in it that will fowl the water. Regular dry aragonite sand is much cheaper and nearly the same stuff. Dont buy any more of it