It seems too late since you've already chosen the classes for the game but I would loved to have a class closely linked to the setting and the souls in particularly.
Why not using something like the Artifiicier from DDO (Dungeons ans Dragons Online) who could use a soul to temporary link them to places or item, the stronger the soul the stronger the effect. If you choose to give souls to other creatures (somehow like the Buddhism), it would be easier to do (like linking a tortoise soul to a shield to make it harder or a barbarian soul to a weapon that would do more damage). That class could also be able to influence and communicate with the souls of the living or the dead.
You could also use this class, let's call it the Soulbringer (another old classic ) to have a special kind of crafting, unique to the setting. The soulbringer could cast rituals to permanently link a soul to a place or an item. Using the "Form and Effects Bonus" from Ars Magica (well idealy, you would use the whole rulebook ) would add a nice touch and you could limit the numbers of great souls avalaible to the player during the course of the game to make the choice of how to use them a hard one.
As I see it, the soulbringers could be revered by certain cultures and for them it would be the greatest honor as a funerary ceremony to be linked to an item as it would garanty some strong souls to stay whole after death and some great warriors could still help their people after death this way.
For other cultures, it would be an horror to prevent a soul to travel freely and the Soulbringers would be hunted without mercy by them.
Add to that, that with such a class, strong souls like those of the pcs would have great valor and it would create lots of interresting situations.
I never liked D&D magic system but talking of "Rest spamming" in IE games is in my mind a fasle problem and boils down to lazy design from the developpers. It's because the gaming world in IE doesn't react to the rest mechanism that there is a problem. If your party decide to leave halfway through a dungeon populated by drows to sleep, you should expect those drows to mount a hunting party and if the pcs casualy sleep in the open that should lead to a depleasant surprise. If they do the same in some caves infested by Kobolds, the kobolds should prepare some traps, or flee if they have the occasion. A bandit chief could flee with his treasure during the pcs rest, letting his men to dye and cover his flee. That open a lots of possibilities. A rpg is about choices. You should be able to rest when you want but those rests should have some consequences. Ennemies should regroup wich means for the player having to choose between going on in a battered state or being rested but having to face bigger groups ready and waiting for them.
