My response is mostly speculation. I'm not a art person but I' am an aspiring poet. With poetry, you can free lance and try to sell your own original work. Mostly for legality issues, you have to have your work notarized or copyrighted. If you want to sell original work at an event, you need to coordinated with the event. Like a convention, i assume you have to apply for a license for a stand at the convention. Fan art- thats tricky. Because from my knowledge and experience, you can't profit off of fan art. That's making money off of someone's else name and you're liable to get sued. I assume to sell fan art you need some type of permission. But at a anime expo i assume it's allow because everything is themed- but again you probably need a license to host a stand or booth or something. But! This is all speculation. The best thing to do is try to research on government sites or just ask people you see at conventions selling fan art. If your a college student, I'm sure some professors can help you and if it's like my college they have specific outlets, like exhibits and expos, to help get your name out there. Network would be my advice.