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Your indoor cage should be that size and that’s the smallest size if they aren’t free roaming. Free roaming rabbit can have smaller cages as a home base.
The litter box should be as big as a normal cat litter box. Myself use recycled paper pellets and it reduces order quite well as long it’s not my giant bunny going. You only need to have a news paper in the bottom, paper pellets on top and hay. Best to conceal the urine odor.
Also cleaning the litter box every other day will help, I only clean my litter box once every week. But the optimal would be twice, to not have any smells in the room.
My indoor cage, won’t let my bunnies play or binky in it except for my small bunny but he’s weight 700 grams and overweight. So my indoor cage can let him play in it but not for a normal size bunny.
Because you live in USA I would recommend you to build a cc cage. For an indoor cage instead, it will be cheaper and you can give your bun more space.
If you can’t provide a bigger cage or let your bun free roaming. Maybe you should consider letting your bun find another home. So it can get everything a bunny need.