I am playing something very similar to that myself right now. I am a cleric and will go prc into 'pale servant of Azerot' which is basically the opposite of Pelor. We have our own pantheon and Azerot is my goddess.
My character is Necropolitan in a very city heavy campaign and here is my characters kinda story/limitations:
When people make deals with the devil or death, someone needs to collect those debts and thats what my guy does. He goes to the people that say they would give anything for their child to make it through childbirth if born sickly (this just happened in the game). Right in the middle of a session I get a note from the DM saying that my goddess has called me to go an collect this debt and basically I have to go out and death knell a town guard that made a deal with death.
The way it is rp'd is that the more frequent I 'collect' these debts, the more human in appearance I become. The longer I go without 'collecting' the more undead I appear and attention I draw.
as for the prc we are switching out some of the abilities so that I can use certain life absorbing spells (death knell, vamp touch, consumptive field as sla's) and I will also be getting spell stitched to do that.