A: Cats love getting scratched so it's an awesome idea. Some people make "teeth" for these catholes. It's pleasant for a cat to get scratched so it's more inclined to use the hole.
A: The brushes pick up loose cat hair.
A: Use an electric jigsaw or a hand coping saw would also work (although it would obviously be slower). A coping saw is less than $10, if you do not have one personally, or one you could borrow.
A: Jig saw
A: No - there is not. It is for an interior door.
A: There is no flap or cover on this opening. The arch is made of wood. The base of the brush is pliable plastic making it easy to remove for cleaning.
A: no. I was disappointed. Hope it works