Can bulletproof glass be used as plates in a plate carrier?
Could? Yes, though I'm not sure they would be as effective. Should? No, though I guess if you found some lying around and didn't have actual armor it would be better than nothing.
Sure. We had a pile of offcut 1" material from penitentiary job. Spent evening with dad and buddies shooting it up. 22lr barely penetrated. Desert Eagle didn't go through. 243, 30-06 went right through, you could see the spin on bullets.
We decided prisoners most likely would have pistols at best. And this way guards could shoot them through glass with their rifles if needed.