Make sure that if you get a peacock, you are using soft lighting. Too much light can lead to shell disease for peacocks. Very subued lighting and lots of live rock and rubble is needed, and make sure you cover that tank. My 7" peacock jumped one day. Luckily, I got her back in and she recovered nicely. I don't think a built-in overflow would be any problem with a peacock. Make sure you put that heater in the sump and not in the tank itself.
For what it's worth, G. ternatensis is an AWESOME animal, but they're a little more difficult to find sometimes.