can someone give me advice on setting up a herbie overflow

[megs_clark]

I recently bought a 72g bowfront and want to have it drilled. I can bring it to aquatic addictions for drilling @ $25 a hole and they will do the overflow for $45, But Dan is not that familier he said with herbie overflows. So i was hoping for some advice, I want to put in two drains to the sump, the main drain and the emergency drain. And 2 return drains? I tried googling this for hours but not many diagrams with single overflows. My question is where is the best place to have the holes to the sump drilled, in the corner or center, and should i have all 4 holes drilled the same size? I read to either get 1 1/2 inch bulkheads or do 1 inch bulkheads and use 1 1/2 piping. Is it hard to silacone your own overflow in, should i just get them to do it. I also read silicone doesnt work well with acrylic, so was wondering what one uses to attach a overflow box to the glass tank. And last does anyone have any pictures of their herbie style overflow with a single overflow i could see, or any good sites with pictures. I see alot of talking about it but not to many pictures? Any help would help :O) Hoping to drill it this weekend
Also do i need 2 returns or can i get one and just use a couple korelias for more flow in the tank