I am about to enter my first historical game...
which is also my first Iron Heroes game...
which is also my first play-by-post.

I have to say, I'm really stoked. It's set in Sassanid Persia, so you've got all kinds of ethnic groups to choose from without being too terribly hindered (Jews had a small amout of political clout and Christians were still sort of okay, except for the whole Roman affiliation, plus Zoroastrianism (best of all dead or near-dead religions) was still alive and kickin').

I also understand that there was one theologan who broke with the Catholics on the issue of whether Mary was really all that important and fled to Persia, and that many Catholic clergy were assassinated so that the non-Roman offshoot of Christianity would prevail.

I read this and thought "Man, I wanna play me a priest-killer."

I am so friggin' stoked on this. I'm not really sure what ethnic backgound I'm going with, and I'm stuck between whether to play a harrier or an executioner (I'm leaning toward the latter). Also, kind of wondering whether I should do the whole addiction to hashish thing. Did that happen earlier? Later? Not in Persia? Either way, it would be cool.

Anyway, as I am a noob on all fronts (except maybe D20), I was wondering if anyone had any input. What backgound does a priest-killer come from? What class/traits fit? What exactly are the stats for hashish? Anything really.

I'd say take whichever class better fits what you want to do with the characters.  The fluff of the priest-killer job can be added to whatever class gets the job done.  As to the stats for hashish, I seem to recall vaguely that someone has done a big d20 PDF on the effects of real-world drugs.  Maybe I saw it on RPGnow?

Yeah... already decided on executioner with the bloodthirsty and child of faith traits. Good stuff.

Also, anyone know any good information regarding the time period? American schools tend to neglect Middle Eastern history...

I can't vouch for it but wikipedia has an extensive article, with references, on Sassanid Persia.

One thing I came across a while ago, which I'd never heard of before, was the story of Mazdak, which kind of has to be read to be believed.

I think that hashish isn't well documented until after the fall of the Sassanid dynasty, but there are some hints that it may have been known much earlier. E.g., some think that it was used as part of the rituals at Delphi in Greece.

Yeah. The wikipedia bit was where I got the whole priest-killer idea... hadn't thought to check their referrences, though.

I don't know about hashish at Delphi one way or the other, but I do know that over the last couple of years it has been established that Delphi lies over the juncture of two faults that conduct up psychoactive hydrocarbon gas through a spring.

I didn't know that Aos--I just did a search on Delphi faults. Very interesting. The gas is ethylene, which is also produced by ripening fruits. So next time you need inspiration, stick a bunch of bananas in a bag and inhale deeply.