Aquarium in the wall
There will be a lot in common with framing a window.  Here are a few things to consider:


Make sure the floor can support the weight of a tank full of this much water.
If you're on concrete, or think there's even a remote chance of moisture from the tank getting to the wall, I'd use pressure treated wood.
Consider how you will access the tank once it's inside the wall.  I think a false wall building out the side of a room with a closet door to access the tank from behind would be easier to maintain.