the volume you stated is correct at 5026 gallons, but that is if the tank is completely full. you will have some unused volume at the top. if you leave 6 inches of dead space at the top, you will have 4712 gallons. the water it self will weigh 37,700 pounds (assuming 8 lbs per gallon). then you will have to add that weight of the tank (probably several thousand pounds), as well as the displaced weight of rocks and sand (obviously they weigh more than the water volume they are replacing). the point im trying to make is that this thing is going to be unbelievably heavy.
there is no way this is going to go on anything other than a concrete slab. and it will have to be on grade... you will also need to add concrete piles under the foundation to support this tank. ($$$$)
how tall are you ceilings. you will need to leave some space above the top of the tank in order to get stuff into and out of the tank. i would leave a couple of feet above the tank. plus, you are going to have to deal with lighting up there too.
with the volumes you are talking about, you are probably looking at commercial grade equipment, and an entire room dedicated to just the equipment. and not a small room. the amount of top off water you are going to need on a daily basis is massive.
with a tank that deep, you will probably not be able to keep corals. 400 watt MH
lighting is only really good for tanks that are a few feet deep (i.e. 3 feet). so, youre probably going to be limited to fish and inverts.
here is a link to take a look at... it is a 1700 gallon plywood tank with a single viewing pane. it should give you some ideas for the construction methods.
do you have a budget for this project? will you be doing the work yourself or contracting it out? there are so many other things i could write, but thats enough for now.
while i admire your project, i think it is a bit over ambitious. but, im willing to let you prove me wrong! :P