No, you do not need to post bios first, but please post it at some point. Though you don't need to include everything, things can be kept secret if necessary or if you wanted to leave some mystery.

To answer the next question, you can be literally anyone. Apart from the obvious, like other peoples characters or gods etc. No, you don't have to show up at the council meeting, but whether you do or not will have an effect on how the plot develops.

As for other people, a few friends of mine are interested but don't as of current have the time to join in properly. I hope to have a few more people over the course of this week also interested so that we can have a small group of people posting at a decent pace to keep the roleplay moving. 

There'll be some other characters joining in and making some sort of influence quite soon as well, though dependent on how it develops there are several outcomes and possibilies which are also dependent on how people choose to go along with it. 

Sorry for any annoying blocks of text, bad habit.