If you want to flow that much water, use full siphon, not a gizmatchy on a stockman or durso style drain pipe. BeanAnimal's S&FOS system renders such things obsolete, in terms of performance, adjustability, and after initial setup, is set it and forget it. You are already planning three holes, so make them work for you, rather than you work on them.
An overflow box that size, at these flow rates, will pull more subsurface water than surface water. Organics collect at air/water interfaces, (why a skimmer works), so you want the "surface water" out of the tank as quickly as possible. The longer the overflow or "weir" the thinner the sheet of water "overflowing", the quicker the organics get to the sump for processing.
4 - 1" returns is roughly equal to 1 - 1.5" pipe as far as area is concerned, however, the associated fittings pipe, and such, will add additional friction loss to the equation, reducing your flow rate.
The question you need to ask yourself at this point is: Do I want something that will get me by, that will work? Or do I want something that will work well?
Regards,
Jim