How many holes is too many?

[mr_alberta]

Well, before I hack away at the glass in my tank like a blind woodsman, I want to make sure that this is feasable:



The glass is, I believe, either 1/2" or 5/8" thick and is 45"x30". I want to cut a slot out (I was thinking 16"x1 1/2"?) and use an external overflow. Is this too many holes in the back glass? I may add another larger hole as a closed loop intake (or make the overflow slot bigger so I can put the closed loop intake in the overflow box). The faint gray line is the potential overflow box.

The reason for the external overflow box is space. Since the tank is only 19" deep, I wanted to maximize the space useable in my tank.

Now, this many holes won't structurally weaken the glass to the point of having a possible blow out or anything will it? Thanks for any suggestions.