Actually if you're using those rules I'd give the wizard the fourth spell set as standard, or he'll be quite a bit weaker than the others. I'd make a wizard only artifact for the three chaos sorcerer spells that can (or does) cost him MP when he casts them. I think they need the upgrades to match your elf, an extra spell set at the cost of -1BP/+1MP and unable to use the battle axe and plate armour that have major penalties anyway.
The wizard picks a spell set, the elf picks one, the rogue picks one, the wizard picks one, the elf picks one and the wizard gets the other two. I bet the wizard will end up with earth, fire, protection and detection, the elf will have water and darkness and the rogue will have air.
But then you're going to have an extra hero and they'll be improved over the standard ones, so you could give them the abilities that Berien came up with from this thread:
http://forum.yeoldeinn.com/viewtopic.php?f=38&t=2351 and/or the increased BPs that I'm going to use: Orcs/Zombies 2BP, Fimirs/Mummies 3BP, Chaos Warriors 4BP, Gargoyles 5BP.
I'd also be tempted to add +1 movement (squares, not dice) for the elf and -1 for the dwarf.