I don't think you need to change the lore to much, as far goes as the Elves and slaves, as it isn't an uncommon practice to imprison those that could throw a wrench in the war machine. The US did it during WWII with the internment camps, though they weren't slaves they were still prisoners of war. Looking back on it it is ridiculous and horrible to have ever been allowed to happen, but at the time it only made sense since we were in a two pronged war that we weren't sure we would win. Drawing parallels between real life and the Elven/Human War shows that during war time, especially when everything you've got is being pushed into the war effort, sometimes hard choices have to be made. 

Though I do disagree with the multitude of executions you hinted at happening [i]after[/i] the war was done. That seems like it'd be a horrible decision, as it would surely just reignite the war once more. Especially since King Erik would take it as blatant disrespect to himself, seeing as they would be his soldiers/citizens that were being executed after a peace treaty was signed between the two kingdoms. Just my $0.02 on the subject. Don't mean to add anymore work on your shoulders, being you are the GM after all.

Also, as far goes as starting, I think the king/queen of each faction should be in place, since they'll be the ones pulling the major strings throughout the story. One RP I showed interest in is now starting to feel boring to me, so I wouldn't mind writing a CS up for the Vampire Emperor. I know you don't want one person writing for two spots on the major roles, but being that the vampires are working behind the scenes and are out to crush both the Elven and Human kingdoms, it wouldn't be that hard to write. I have experience controlling characters that are opposed to one another in other RP's, so it wouldn't be new for me to do. Though I understand your rules and will gladly wait for more people to show up to claim the roles. I'm just excited to get this one going is all. :dreamy