Nails, yes. Good for the furniture, good for your skin, good for the cat. Back nails seem to need it less than front nails.

Litterbox, I have new cat’s inside a cardboard box so only one side is open and that side has a sisal mat in front of it to help catch litter. It cuts down on litter being tracked all over, but some will always stick to the cat’s paws.

The only cat poop I’ve encountered that smells was senior cat, who occasionally had diarrhea.