How big is the coop you bought (feet by feet)? Honestly, I'd only get two - especially if your're getting Orpingtons, as they are a larger breed. Those prefab coops in my opinion advertise to hold more than they comfortably should. I see you're in the south, though, so that should help as they can go outside all year long. I'm in MN, and my chickens spend the better part of the winter inside the coop, so I want them to have plenty of room. I do wonder how hot it gets at night for you, though, and if they'll have enough ventilation and air movement.
Whether you have 2, 3, or 4 hens, you won't need more than one nest box anyway. I have six hens, eight nests, and they all want to lay in the same one.
Yes. Raccoons will kill chickens, as will skunks and oppossums. If your coop/run/tractor is made with chicken wire, you will want to replace or reinforce that with 1/2' hardware cloth. It's much sturdier than chicken wire.
Orpingtons are fairly calm birds and lay nice eggs. Will you be getting adults or chicks?