I have a 5.5 going now but it's a normal rectangle tank. Since you have a hex it is going to be extremely hard to fit a
powerhead in it and then puting
LR, that's going to be extremely hard. You probably won't be able to get any fish either and water levels change really fast. If your up to spending lots of money then go ahead. I've spend couple hundred dollars already on my tank and I still need livestock and corals not to mention getting a
skimmer later on.
I don't know what you have with your integrated kit but you will need
power head
5 gallon bucket+heater+small powerhead (to make salt water)
live rock
It's hard to say what you will need depending what you have already.