1) You may one apply for ONE Main Character from the list. If you are already playing the character you wish to apply for then you'll get him/her but no one is being allowed to carry on with two as it's unfair to people with only secondary characters.
2) As for secondary characters, they're not mandatory but it would be nice to get a fuller cast and within the RP world they can be as important as you like.
3) OC characters are accepted, but they might well be rejected for the moment. We'd prefer to keep it just to the Downton characters however if an OC fits into the Downton world well then we'll make exceptions. We're just trying to avoid and influx of Mary-Sue's really.
4) PM me your application rather than replying in the thread. I have a feeling that should certain characters become available then there will be demand for them and I think it's only fair for anyone who wants to apply to be able to do so under their own terms. This is mostly for the sake of the writing samples.