I agree with Czech that zombies should be the focus of pestilence, since it would make a perfect disease for the scenario, so that's where I'm throwing m vote.. That being said it could also work for death (The rising from the grave kind) if the contagion idea wins out. 

I have a suggestion for the Death finale.The reason why I brought up the different characters for each scenario was mainly because I thought the idea would work better that way, but with a few tweaks I think it could work. The idea is that basically after the Famine scenario(that is if we're doing he horsemen in the order they emerged from the seal if not than whatever the one was before death.) the characters discover that they A) all died at the end of the previous scenario or B) Find out they've been dead the whole time and that maybe the previous scenario's were a test from the horsemen to prove humanity's worth or something. After figuring this out the last scenario is them escaping Hell/or the Underworld perhaps while being chased by demons, deceased souls, or Death himself. 

I also have a small suggestion for famine as well, Maybe an unnatural massive swarm of locust? They are usual the personification of famine after all.

These are just suggestions. I'll tough out through whatever we end up doing.. We've got a bit of time to work this out after all.