Goblins should be our main characters, but we can and probably will have to play non-goblin side characters at some points. As for the RP, it is more of a sandbox than anything else. I had no overarching plot in mind, but events will unfold as I and the other players make happen. If things get too out of hand (like if one of the players has aliens land and take goblins to another planet), I'd step in and have those posts edited, but as long as the story stays within certain broad parameters (those of fantasy and being fairly serious), I wouldn't usually intervene.
Our characters can and should evolve, but they still have to be true to their species. For example, Breden has gone from being a poor hunter to a good one, but he still wouldn't be caught dead willingly using a human-sized sword or axe. He'll never be more than three and a half feet tall, you see. Same thing with his culture; even if he could find some shoes, he wouldn't use them.