It will be hard to keep things balanced with evaporation. You'll need a seriously huge ATO on a big system like that. As in the return pump will be the size of a regular sump return pump.
Additionally you may have problem with actually balancing the pond itself properly. That's a lot of water and it's going to have to be all tap. Big SW
ponds like that are normally kept by people that live next to beaches (easy water change) or teams of aquarists like in a public zoo or retailer or company that can hire maintenance crews. An indoor sw
pond may work...idk about outdoor.
I'm also wondering what happens when it....you know..rains.