Using the following input parameters
Gallons per Hour = 1000
Drain and Overflow sizes are calculated as
Recommended minimum drain pipe diameter = 1.31 inches ID I would go with two pipes in case one plugs
Recommended minimum linear overflow size = 15 inches (This dont apply if your drilling)
Where you place it will depend on your wave-makers if you plan on a standing wave then it's better to have the overflow in the center. For the return you will want to match it to your drains, be sure to account for head loss. just dont go over