If I were you I start looking at your product first. Have you ever created a map pack? or a d20 adventure? d20 is nice, because you can use the rules if you do it right. That's not terrible difficult. I can help you with that.

I think it's a good start to see if we can do it for free. Under a Creative Commons Licence for example. see here for licences

Then if this is succesfull, you can see if there is some money in it.