If the bottom of the tank is labeled "tempered" I would bet that the sides are not. It would be highly unusual for the tank to be all tempered glass. Highly unusual but not impossible.
PVC overflows can work in higher flow settings like a sump but can be (usually are) problematic long term.
An alternative to a sump and drilling the tank is a dump filter...which is basically putting a sump on top of the tank, pumping water from the tank to it and allowing water to "dump" back into the tank via gravity.
I use actual sumps for my big tanks (just on the top of the tank and set up as dumps) but other people use nice-looking planters and the like so they look nice.
I'd bet that Joey has plans for them as well (they're quite simple).
Window planter boxes work well: