Help choosing air pump 4 bubbleponics

I've had three good grows from soil and am making a bubbleponics setup from a 20 gallon blue plastic storage container. This will be my first grow without soil. I wanna put 4 5" net pots in the lid and grow 4 nice size plants. Shouldn't 20 gallons be plenty for 4 plants? My main question is this: what kind and what size air pump do I need to adequately oxygenate the 20 gallon resevoir? I also want to add a water pump to continuously feed the inner roots in the net pots. Is that a good idea? What size water pump do I need? I have some white widow, rocklock, blueberry gum, kandy kush, exile and one other strain feminized seeds on thier way here so I'm trying to have this ready by the time they get here. Thanx!

Go to Walmart, and in the fish tank supplies section, get the dual output air pump, it will be sufficient for the 20 gal container you have. I have an 18 gal container, and it really makes the plants thrive like crazy. Get a couple good airstones too while you're there, I went for the long blue ones and they rock.