Fill our world with life!
We have been discussing about human beings so far (the consens being that there should be no elves whatsoever). What we are trying to build with all the discussions about religion, regime, technology etc. is the system of the culture Threshold is situated in.
However, there may be other human civilisations, other cultures in our world. Maybe we need not define them clearly from the beginning, but I think it makes sense to sketch them out and mark them on the map. They might affect our characters indirectly, and we might want to use them later in the story.
Second, what "unusual" creatures are there in the world? If elves of any kind is a No-Go, does that mean anything "unusual" is as well?
What about the sea monsters Wolfshade suggested? Should we define all the creatures from the beginning or rather define a rule what kind of creatures are allowed to create while we are going (for example "unusual but not intelligent" or something like that)?