What size is the barbed fitting?

I found fittings that worked with this pump at my local ACE Hardware.

How loud would this be inside?

I use mine outdoor, submerged. The only thing I hear is thrush of water over my waterfall. And I have run it 24/7 for over a year with no problems. I bought a second one to drain my jacuzzi. Great product, & very dependable.

Is there a filter screen? What size and how much debris can it handle?

No filter. The pumps propeller is directly underneath the pump so I suppose the black foot piece does filter out bigger objects. I use the pump for my hydroponics table. It does work great and pushes the water from my tank underneath my deck about 12 feet straight up to the table. And I haven’t had anything clog it or any other issues. But if you plan on using it in an environment like an outside pond it probably would get clogged with pond debris. But for the price you could make a filter out of cheese cloth or something similar. If it’s for a pond you could put the pump into a plant pot like one of those plastic black ones and then cover the top with cheese cloth and small gravel. Best of luck

can this be used to pump out a 2000 gallon garden pond for water change?

If your not concerned about how long it takes, I used it to pump out a much smaller volume and had to switch to a different pump. I used a Master submersible utility pump, model 540094-01, 1/4 HP, also available on Amazon, but about 4x more expensive. The FREESEA was taking forever. The Master pump has a garden hose size output.