I'd go for the opening on the side, that way you won't have to worry about the snake getting bigger and getting stuck in the top opening. Otherwise I don't think there is much of a difference, but I'd stick with only one opening.

I wouldn't worry about the rough surface either. Most of mine shed inside their smooth plastic hides, with almost perfect results. So, a 'rough' surface is not required for a clean shed.

As for size, that's going to be hard to judge without seeing your snake. I'd take a couple plastic bowls and try them on for size. You want something that is nice and snug without too much head room.

I hope that helps a bit.