Drilling holes on a 75 gal tank?

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I'm getting ready to set up my new 75 gallon tank. I e-mailed Perfecto and they said that the bottom pane of glass was the only tempered glass. I want to have a overflow to a 33 gal sump with a return as well as a closed loop.

How many times turnover should I try to get through the overflow to the sump and back? I can use the drain overflow calculator http://www.reefcentral.org/calc/drain.php from reefcentral to figure out my bulkhead sizes from there. But should I put the drain lower on the back pain of glass and run a standpipe up to the surface? or should I put it right around the water level and drain straight into the bulkhead (with a screen of course)?

Next question is how much flow should I try and get from the closed loop? I'm thinking around 1500 gph total (20 x turnover). So I guess I can figure that out once I decide how much flow is going through the sump. For the bulkheads I was thinking one intake and maybe 2 returns. Then split those 2 returns inside the tank possibly with lockline tubing. Does that sound good?

For a closed loop can I just use the same size bulkhead as the fittings on the pump? Same for the return from the sump?

Thanks

Myles