Here at PD RP, most people allow more then one character in an RP. We know that most people don't like telling the story from one characters perspective, and want to take part in all sides to see who they like best.
Just make sure you don't run into something that can lead to disaster, too many characters. 4 characters is a lot, but some people will make that many, and possibly more. The thing is, when you make too many accounts, you cannot jump from one to another as fast as having 1 or 2. When you have several players, you start focusing on one too long, and might loose or forget another.
But don't let that scare you into making only 1 person. Having more then one can also be fun. It makes the role play experience that much better. When you have one character, you don't get to see what it's like for another side. When you have multiple accounts you can be evil and good, and see both angles of the story. It really is so much more entertaining when you can be on multiple sides, and efficiently fight yourself!
The bottom line is this, multi-characters make the experience a lot more fun then having one for many people, but having too many can lead to disaster and possible banishment from an RP. So there are pros and cons, just like any feature, but it's all up to you.
Adaption from this thread on Children of Ivalice