Should I stop selling fanart if I'm actively taking part in a mainstream production right now?

I'm not entirely certain, but I think that selling fanart is okay as long as you say that the characters don't belong to you. After all, everyone at those anime conventions sells that kind of fanart stuff, i highly doubt they went through all the trouble to get the copyrights over the characters, HIGHLY doubt it. Also, why do you have to pick one or the other? Just sell stuff at the conventions when you have time and then fall back on your career. I mean, getting a job will just open doors for you in the future, since you will be able to make connections.