There are no restrictions except when it comes wizards/mages. Magic users are as rare as the blood type -AB blood type so there will be only one maybe two if you make a good argument. I just would like characters to have some sort of elevation in he army.

The Elven Duke/Duchess and Baldric are the closest of friends but other wise it's up to he players creativity.

You can make your own faction. I have no problems with that.

Characters can be a Korilan survivor, an Avernian knight looking for glory, it's up to your discretion. I just mentioned the major players up above.