Oh, it's no problem! Most of this was pre-written. That's why liches are included in there (I mean, if you want to write a lich, all the power to you, but I wouldn't expect it) and other stuff that probably isn't relevant. Your chara being the one who stumbles upon the henge is usually what I anticipate happening, and of course you can write more than one character.

As far as ethnicity, culture, and race goes, yes, it all exists. Riverain, the setting we're in, is where I imagine that meltingpot to be - but that just means there's no common face in Riverain, not that everyone looks and acts the same.