I'm pretty excited. There's still some open questions about the tank, most notably how I'm going to light it (it's so wide!), but those will be answered when we get there. The next thing to take care of will be the sump.
The metal stand is being custom built to be a total of 40 inches in height, with 2 inch steel beams. That gives me a 'usable' footprint of 68 X 30 inches of floor space under the cabinet. I want the biggest sump possible, so assuming I need a half inch of clearance between the base of the stand front to back, and 12 inches of open space on the long ends for any equipment that can't be in the sump itself, the sump will be 56X29 inches long.
I also want the sump to hold as much water as possible, I want the sump to hold as much water as possible so if I make the sump 20 inches tall, I can keep the water at 12 inches when the sump is running without risking overflowing the sump when the tank loses power. When the aquarium is turned off, I should have roughly two inches between the top of the water and the lip of the sump tank.
Here is my crude first draft for what the sump will look like. There's going to be two compartments, and the water will flow in a U shape from the point it enters, to the point it exits the sump (green line). I'll be able to turn the gate valves in the middle of the sump isolating one half of it from the tank, with an alternate route for the water when the gate valve is closed (red line). That will allow me to pump all the water out of one half, fill it back up with fresh water, add salt, mix, then re-open the gate valves returning the new salt water to the main system.
I'm trying to decide what skimmer I can fit under that cabinet (it will likely need to be on a 2.5 inch stand) so I can work out exactly what I need in terms of space in all the compartments.