This is great! The only thing I'd recommend is using an image map with a coordinates tool as it's way quicker for something like this. However, you have my thanks x1000 for explaining slicing as it's a very handy thing to know for other things.
I always love these things but get frustrated trying to make them. So, I'm one of the people who hugely respects games who manage to pull them off and well. I especially LOVE the one for Neville's room. I've seen people link pictures but that seems to be a clever way that takes up less space. :D