Not to be a downer, but honestly, I think I'd much rather go with a traditional tank/sea-world-type-aquarium setup. Something raised up, maybe on a stand, with a main front viewing panel, instead of that massive of a lagoon. Keeping with your dimensions, something like 14' long, 6' deep, 4' tall would be about as cool as possible. That way, once it's all finished, how awesome would it be to sit back in a super comfy leather Lay-Z-boy and watch the tank, instead of having to sit on the tank rim, trying to peer into the tank, trying to see the fish/corals through the waves/reflections...