I'm sorry, I've always called a crate a kennel. Yes, it's recommended that you don't get a huge kennel for a small dog but a boxer will get big very fast.
I'm using one for my puppy and it's rather large for his size but he's never had an accident in it. Of course, he's only in it at night or on the rare occasion we all have to be out of the house. He actually loves his kennel and goes to it when he gets tired at night.
I haven't ever used a litter box but I know people who use pads and papers, etc. and it works for them. The only reason I never used them is that there has always been someone home to walk our puppy every couple of hours. Otherwise we'd have to use one, too!