42mm is I think pretty close to 1-3/4" ? It will probably work OK but just eyeball the hole saw to the bulkhead before drilling I guess - it would suck to find out it's 1mm too small or something.
I'm not sure if closer to the edge increases the risk of a crack. Go slow and easy and real gentle on the pressure as you're just about to poke through. The times I've cracked glass while drilling has always been at that point where it just breaks through to the other side and I suspect in each case it was because I lost patience and pushed too hard. If it's your first time drilling maybe try a practise run on some scrap glass. It's really not too bad though, just slow speed and gentle pressure and basically you sand or grind the hole out rather than "drill" it out per se.
Polarised sunglasses are where instead of tinted lenses you have little microscopic lines running across the lens. It's to help reduce glare off reflections of sunlight. I'm not sure if you can get them cheaply, I have coke bottle glasses and usually have to spend a few hundred per pair of glasses so getting the polarised lenses for shades is doesn't make a signficant difference in the cost so I have them but have no idea what the uplift was for that, sorry.
When you look at tempered glass through polarized lenses you can actually see the checkerboard pattern produced by the tempering process.