Guildenstern's ideas seem the most sensible here for a while. However, I would dispute his division of Christianity. Mormonism is ridiculously minor to include if you're missing out Ethiopian Orthodox and the Church of the East. Remember, there are three great branches of Christianity - Protestant, Catholic, and Eastern - including those Eastern churches that are technically not Orthodox (Coptic, Ethiopian, Nestorian). Mormonism is also a lot less important than Anglicanism, if you're going to have different representatives for all the Protestants. I would also suggest Jewish Christianity, since this, not Greek Orthodoxy, was actually the first version of Christianity. And also the AICs, which in some ways may be the future of Christianity. I would also vote to add the Kakure Kiri****an, not because they're important but because I like them!
I might add to ImpressEmpress that Theodora wasn't "orthodox" at all, but a Monophysite, and Justinian was of course an Aphthartodocetist, at least at the end of his life... time to add the Copts!
Incidentally, atheism does not mean disbelieving in the supernatural. It means not believing in God. You could, in theory, believe in supernatural things, but not God. An example would be the philosophy of John McTaggart in the early twentieth century. Moreover, it is wrong to oppose atheism to "religion". Atheism is opposed to theism, and religion need not be theistic. For example, Theravada Buddhism is generally accepted as a religion, but it does not involve belief in God or gods. Westerners always get hung up on this. The theism/atheism dichotomy is a feature of Western thought, and Asian belief systems do not fit into it - for example, Hinduism is certainly not atheistic, but it's hardly theistic in the usual sense of the word. Westerners tend, erroneously, to suppose that religion is always about God, and if you believe in God you are religious - whereas in fact belief in God is simply one aspect of some religions.
So I think it's wrong to have atheists as the barbarians in this mod, because atheists are not necessarily irreligious, and religious people are not necessarily theists. You should have barbarians as simply secularists, or unbelievers.
I might add to ImpressEmpress that Theodora wasn't "orthodox" at all, but a Monophysite, and Justinian was of course an Aphthartodocetist, at least at the end of his life... time to add the Copts!
Incidentally, atheism does not mean disbelieving in the supernatural. It means not believing in God. You could, in theory, believe in supernatural things, but not God. An example would be the philosophy of John McTaggart in the early twentieth century. Moreover, it is wrong to oppose atheism to "religion". Atheism is opposed to theism, and religion need not be theistic. For example, Theravada Buddhism is generally accepted as a religion, but it does not involve belief in God or gods. Westerners always get hung up on this. The theism/atheism dichotomy is a feature of Western thought, and Asian belief systems do not fit into it - for example, Hinduism is certainly not atheistic, but it's hardly theistic in the usual sense of the word. Westerners tend, erroneously, to suppose that religion is always about God, and if you believe in God you are religious - whereas in fact belief in God is simply one aspect of some religions.
So I think it's wrong to have atheists as the barbarians in this mod, because atheists are not necessarily irreligious, and religious people are not necessarily theists. You should have barbarians as simply secularists, or unbelievers.
I had to chuckle at the thought of Atheists being barbarians in the game., as they're not viewed as a religion. 
