Since everyone is giving advice on tank size, I'll weigh in, more water volume means longer build up of toxins/detrimentals giving you more reaction time to counter any issues. In aquarium keeping Dilution is the Solution to so many things. The best advice I can give is plan a Sump that is at least 50% the size of your tank, I hit close to this mark myself, I have a 300g display with a 125g I use for a sump, total volume is about 360 gallons. Large Tanks have their own set of challenges, one is the sheer weight of the thing, big tanks must be on ground level, or in the basement like mine. Being able to reach into all corner of the tank can be challenging as well, especially if your vertically challenged. (That means GOD built your butt to close to the ground shorty).
And the price of everything is more because you need more of everything, but the reward is that much bigger as well!!
good luck to you.
Don't buy a RED SEA!!
:)