There is tons of info on this. Every tank is different. All risk failure.
I was taught this is the way to do it:
The rule of thumb is that the holes should be no less than 1 1/2 times their diameter from the edge and from each other.
There are other rules you might consider:
https://www.customaquariums.com/information/glass-hole-cutting.html
here are the
minimum requirements in regards to distance for drilling glass
x = 1.5 t
y = 4 t
t = glass thickness
measurements are taken from the outer most edge of the hole closest to the edge of the glass.
single hole along side: x from edge
single hole near corner: x from first edge, y from second edge
holes next to each other: x from edge, 4t apart
holes next to each other next to edge: x from first edge, 4t apart, y from second edge
Holes need to be a sufficient distance from the edge of a pane of glass in order to retain the structural integrity of the tank. The diameter of the hole is the measurement that determines this. From the edge of the glass to the edge of the hole, there should be at least the diameter of the hole in distance. From the center of the hole, it works out to 1.5X diameter. Holes in proximity should be 2X diameter apart on center.