It's the cornsnake we're concerned about with the quarantine; you don't know what the BP could have and possibly transmit to him. Ideally they should be in separate rooms and none of the same equipment would be shared between them, and you'd wash your hands between handling them. If you can't do that, do as much as you can for 90 days. If no one is sick at the end of 90 days, you're good.

For the hides, check out the picture/tutorial Deborah posted. He's going to be growing quickly and outgrowing hides. You probably don't want to bother buying anything good looking or expensive for now. Those flower pot bottoms that she suggested come in a lot of sizes, so just pick the one that is the correct size for your snake (bcr gave you info on how to pick the right size hide).