PuppyGoHereDog Litter Pan (Black, 20" x 15" x 5") Suitable for Dogs up to 6 lbs.

I have a 20 yr old cat who is having difficulty now getting out of a cat box with 5" sides. What is the depth of the entrance side of this box?

On the jumbo box, what is the (l x w) dimension? i want to put a pad holder inside so the walls will prevent my dog from peeing outside the pad.

Is this too tall for a bunny?

What kind of litter do you put in the pan? Is there a specific kind?