hi!!!
My first suggestion, cuz you're gonna get told this a bazillion times, is to check out the stickies in the forum for salt tanks.
They have TONS of info on there, and will help guide you through the process.....
Plus......the salt people on here really know their stuff...
side note......if you're doing a saltwater tank, which...I am assuming you are....the filter is basically going to become obsolete for you.....I have one on my tank with nothing in it, just for water movement.....Invest in some powerheads for water movement....and, depending what you're planning to put in there.....a skimmer.
You could plunk in some rock in right away to begin the long...yet rewarding process of starting a saltwater tank.
IME, I started off small..........and it's worked really great for me.
But..I am in no way an expert......
best of luck...