If you havent already purchased the fish, DONT. With SW systems, the first step is to Season or Cycle the tank. This involves getting your filtration setup, and establishing the bacteria that will deal with the waste. With SW tanks, its wise to add at least SOME live rock, which HAS to be cycled correctly if you dont want all your fish going belly up in a week or less. The cycling process, even with SOME live rock and some dry rock, will take aprox 21-30 days before anything can be introduced to the tank. There are many great articles and posts here on cycling.
As to the fish choices, 5 is going to be the limit, with NO tangs. That tank simply isnt big enough to support them. They are fast swimmers that need lots of running room. I've never seen anyone recommend anything less than a 75g for ONE tang, and 125 Minimum for 2. Hippo's are notoriously sensitive/touchy, so i'd stick with a yellow, should you decide to up your game.
Imho, the False perc's are easier to keep than True Percs, and are widely available in the Tank Raised, so as to be healthy. Still, Proper acclimation, and QT are critical. Do not attempt to treat/qt the fish in the tank with your Live rock. It will absorb the Copper, and leach it later, reaking havoc with your CUC.
All that said, GL.