Sounds like a fun project!) You won't have to worry about anything long as you don't sell it. And include in the credits include who the characters really belong to like "©FOX and its related entities" or "Homer and Monty characters are based off of FOX original characters and belong to FOX" I know it's something like this but in different wording maybe.

or just email them and describe what your doing with it.

http://www.fox.com/corporate/terms.htm