One of the reasons you do not generally see tanks that tall is the amount of pressure put on the front (and back) panels will be unreal. They're going to bow, and it'll be incrediblly difficult to brace them reasonably and aesthetically. You could put braces around the side, which would help, but they're going to stand out, unless you somehow incorporated them into a design. Similarly, you could brace the back.
Using the super thick, 1/2" glass will definitely help, but it can only do so much against the weight of water that wants to be on the floor.
You also run into a very small surface area problem, where your oxygen exchange will be reduced. Lastly, having worked in really deep tanks, it's going to be a pain in the butt to clean, especially because of the small amount of access room through the top!
What I would suggest would be to turn this tank on its side. Make it 48" long, 25" wide, and 36" tall, or better yet, 48x36x36. You can better brace this design with a cross across the top, you'll fit lids easier, and it won't be impossible to clean.
Plus, that's a decent sized tank for some of those fish.
