This makes 5. I would let one more join, if they wanted. Otherwise, five is good enough to start. I'll leave it open, just incase there's one more who wants to play, then I'll start a new OOC thread, with more direct rules on character creation, and combined setting detail.
I'm the type of DM who likes to incorporate as much of the character's backstories into the game as possible, so the reality is that I won't have a story until I hear who your characters are. I do have a BBEG, a Crisis, but who you bring to the table will be paramount to the story itself.
Feel free to start thinking about characters, and I'm not going to hold you to any class combinations. If you all want to be sorcerers, then I'll adjust accordingly. If your element is not a major part of your character, then I suggest holding off on choosing one until we see what everyone else wants. If it is, then by all means, choose an element. Part of me does believe it would be a good idea, story wise, to have one of each element, and then a balance between them (monk or druid), but I'm just not prepared to hold the characters to that until I see what you all want to play.
As for an elemental barbarian homebrew, PM me a write up. If it looks on par with the other Barbarian paths, I'll definitely consider it. Especailly depending on your race. If you're a Genasi of that type, then it would make sense that a Barbarian would learn to chanel his rage into the element he's connected to. If not, we can say he was born a sorcerer, but instead of studying magic, he grew up a barbarian and channeled it through his rage.
