Your biggest pain will be keeping algae off the glass of a 6' tall reef. FORTUNATELY the hobby has been devising some cures for that, including a magnet cleaner that looks like an old-style razor, (Tunze makes it). I have a tank deeper than my arm is long and would be lost without it.
The magnet cleaners are wonderful. I use the MagFloat ones on both of my freshwater tanks.
OTOH, with that weight of water comes a diminishing return on glass thickness. Glass thickness on a 100 g tank is about 5/8ths inch. I don't know how much water 5/8ths can hold back safely, but a 12' run may need some bracing. And you may need to go to acrylic. Seattle Aquarium's big display dome is likely that. And it has good visibility.
Doesn't the acrylic tend to scratch really easily?
Here's one other thing to think of: an infinite tank, ie, a cylinder. They require special mounting, because the 'works' have to be in the center, and you have to get access somehow. But it would take up less area, while the fish would never have a turnaround, and the rockwork would conceal the water intakes, etc. There are companies that do that. I got my tank from one such, and it is real, real solid. Heavy. We're going to redo the living room floor soon, and it's going to be interesting. But it can be done. And such future things should be on the planning list. Access. And refurbing.
I have seen tanks like this, but had not considered one. I may look into that a bit more.