Sorry if it's too late, but I just went through this myself. Had to drill two 35mm and two 60mm holes in my display tank. I was nervous as hell and took my time. I tried practicing on some thin glass I had, but that didn't go well. I definitely recommend finding your local glass/mirror shop, and begging them for some thick glass scraps to try on. Mine gave me a nice, big piece of 1/4" plate, and that really made a difference!
As for the bits (saws), I tried several from Amazon, and they were not created equal. The best by far were the Drillax brand. They are a little more expensive than the cheapest ones on Amazon, but the cost delta is completely worth it (in my limited experience). If they have the size you need then I'd definitely recommend Drillax.
Go slow and good luck!!
--Ron