You can under water but not in hydro if your roots are in the water.

There is no such thing as overwatering. It's drowning. How do we explane hydro ? It is the duration of the saturation of the rootball. It rains for days outside.

If you are going to run co2 you don't need out side air.

Be carefull. No co2 in a living area. It can flood a house and kill everyone.
Been there, almost tragic.

Two 1000's. I would just keep adding waterfarms or 5 gallon buckets maybe cheaper.