The Meaning of Life, the Universe, and Everything.
I'm not sure if this is updated or not, but if you have bukkit (You pretty much will have an insane time making an rpg server without bukkit) you can search up MCMMO and use that. It has levels for different skills, fighting and all that stuff. The classes thing you'll need a different plugin such as PermissionsEx or something, and you'll need to know how to use it. PM me about your server, I'd like to visit it!