If you get him a ball, don't leave him in for more than 30 minutes at a time.
Make sure you litter train him, and if you let him out, have several litter pans for him to use.
Ferret Care Guide
Remember that ferrets are very social creatures, like dogs. They usually do best if you have two of them, and you may want to get a bigger cage for him.
<3 ferrets. Too bad they're illegal in California.