Can this be made in one large dish instead of the the individual ramekins?

I haven't tested it, but I'm pretty sure you could make it in a 4-cup charlotte mold or an 8-inch cake pan. I would caramelize a little more sugar (1 cup, same method) and pour a little more than half of it into the pan. Tilt the pan to coat the bottom with the caramel. Add the remaining caramel to the custard. (step 4)

I think the baking time may need to be increased: bake at 350 in the water bath for 10 minutes, turn down the oven to 325 and bake for 40 to 45 minutes, but check at 35 minutes just to be sure. Once the custard is cold, you can invert it onto a large plate.

I think so, but if I were to do that, instead of using 3 eggs and 3 egg yolks, I would use 6 whole eggs. (You can see from the photo that the custard is a little runny. More egg whites will stiffen it and make it easier to cut cleanly.) The time will depend on the size of the dish, your oven, etc. I’d follow the recipe instructions and start checking it at the recommended time. If it’s runny, keep cooking. If it’s mostly set but jiggly, take it out and let it come to room temperature in the water bath before chilling it. If you use a large dish, you will want it to set completely, or it will be extremely difficult to cut into servings. Good luck. Please let us know what happens.