If it were up to me, i would divide the tank into 3 parts . Each part would have its own filtration separate from the others . Then the one on the far left would be a freshwater discus tank. Super heavily planted and tons of DW and one large pleco.
The middle one would be brackish. I don't know much about brackish fish, but i know some puffers are brackish, so it would be a puffer tank.
The one on the right would be a saltwater reef tank. Full of LR
and all sorts of softies and such.
I think the concept of this tank( or tanks) would tell people that here are different ecosystems than the ones above water.
And the filtration itself would be in another room for people to view and learn about, a place to explore all the tiny creatures that make the tanks run. Under microscopes and stuff.
The tanks would be viewable from all sides and underneath for the kids, but the top would be sealed off for maintenance
one would have a sump visible in the filtration room. A live sump with sponges and shrimps and stuff. There would be tons of charts and several people there to explain it all.
Well now that i have covered everything, i think im done lol.