This is a big issue and a wishy-washy one as well. Some conventions are perfectly fine with the sale of any fan art items while others limit the types of fanart you can do, or ban it all together. I've always been wary about selling my Anime based items anywhere but at a con, though I know a lot of people do sell them online. Companies don't seem to have as big of an issue with costumes and cosplay merchandise, because plenty of people do cosplay commissions.
As far as starting an actual business based off of licensed characters, you could have some legal issues. It sounds like such a fun idea though, so you should definitely look into it!
2013 line up!
cons -Tekkoshocon -UBcon -Colossalcon -Blurriecon -Tsubasacon - N.E. Geek Expo
Margo (Despicable Me)
George Washington Lolita (original design)
Nonon (Kill la Kill)
Litwick gijinka (Pokemon)