I've been drawing and laying out designs for some A2 (16.5 x 23.4) and A3 (11.7 x 16.5) size posters to sell at my first Fanime Convention (2010). All of my artwork is original but its based on established mecha series (Gundam,Eureka 7, Code Geass, Gurren Lagaan, etc.). I just wanted to know more about the legal issues of selling fanart.
P.S. are these sizes too big?
P.S.S. is there an audience for this at Fanime?
I can't tell you Fanime policy but I can give you hints at what Copyright law would suggest:
If the characters are truly your own (I.E, distinguishably and sufficiently different 'enough' from the original) or are used for the sake of parody (in a way that can be easily discerned... as in, you can 'tell' it's a parody), then the sale is not illegal. Those aside, if someone can say, for instance, "Hey, isn't this Wing Gundam Zero?", chances are good the legal water you're standing in may possibly warm a bit.
In the Artist Alley, many of the artist there were selling fanart that they made. So I'm sure it's fine to sell fanart at Fanime. As long as it shows on the art itself that there is copyrighted material being used, you should be fine. In other words, there must be a watermark on the art stating that "animeseries(c)owner of anime series"
From what you are describing, there is a potential audience for the artwork you plan to sell. Just be sure to provide something to carry to posters in like a bag or shipping tube so the art doesn't get damaged. But, that option is entirely up to you.
What usually sells in the artist alley is fanart with appealing artwork- style, coloring, characters, etc. Couplings anime characters, gag artwork, and detailed artwork are usually the top sellers.