Is there an evil version of a Paladin?
If I recall well the paladin can be either Lawful Good or Lawful Evil... but since he converted, he should have lost all his previous Paladin spells, so you should give him the skill tree of a warrior-like (or spellblade-like) class.
Also an unrelated question- I've been wanting to start a game for quite some time now. I've seen an RP system that I like the look of, but have never played it. There are no games of it running that I know of. Do you guys think it'd be a good idea to try running it, or would sheer unfamiliarity with the rules ruin it?
It depends of the length of the game and the complexity of the system.
I suggest you to run a "blank" game first, that is to say a very short game (can be completed in a few hours), with a basic plot, just to see if you and your players enjoy the system, to grasp the basics of the system and to introduce this system to your regular/most experienced players.