sruiz,
I just don't want you to make the same mistakes I did! Once the tank is up, it is so easy to listen to those voices in your head that say, "It's time, it's time!" That's also what you will hear from those salespeople at most local fish stores. You are doing the right thing by looking ahead, planning, and asking questions before you act; I did just the opposite!
I loved my porcupine puffers and it broke my heart to see them restricted and unhappy once they got too large for my tank. Look for those that will stay small, like the tobies Amphiprion suggests.