Yes on the sump. I'll add some rock but no sand.
The display tank is a 75 gallon hex tank that is 3 feet tall. So I will add a very deep sand bed and I might try garden eels at some point in the future, if everything goes well.
These mangroves will be going into the window with some additional light as well.
I will use the skimmer box on this tank. I do want it to skim the surface. It might be a while before I get it running. Money is slowing me down, but that is fine. I hope the mangroves grow above the water line by the time I fill it completely.
I need some rock. I'll PM you about that.