Great idea, I occasionally work on a mini version of a tank like this, 36"x18"x30" with 4" popping out of the wall. It looks really cool. You won't have any issues with lighting the bottom with new led lights, they have great penetration, but have more shadow than t5 or MH. I don't think this will be an issue for you, just place the front set of lights as far forward as possible. My biggest concern with the dream box design is the top. With the top glued on top of the sides when a skimmer overflows it will just roll off the edges onto the floor. I would just recess the top down so it sits on the baffles and the sides make a 1/4-1/2" lip to contain such spills. A little water on the floor can be a non issue but a lot creates a lot of damage. If you integrate a floor drain into the sump area that's great, but it could lead to a problem left un knowticed by a tank sitter. This lost water is replaced by the top off and if you don't realize the problem you can crash your salinity and kill the tank in a few days. Skimmers overflowwing is almost inevitable at some point. Mess and potential tank crash can be avoided with a simple lip on the sump.
Given what your investing into this tank I would just cover the walls And ceiling of the fish room with FRP, fiber reinforced plastic. It's sold in 4x8 sheets and is about 1/16" thick, from most lows and maybe home depot, about $30 a sheet. It's glued onto the walls and is basicaly impervious to water, used in commercial kitchens and such.
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