Do temples auto-generate followers? I know the Daimon Lords are priests, but nothing short of mind control seems able to explain how wide-spread the Portal is. It will be a long, difficult task to uproot it.
Additional question, is it worthwile for a priest to study oratory at the academy? how does that really affect preaching?
I believe Vita knows quite a lot about this but I shall try to give highlights. Surely read that wiki page, for if that is still up to date.
I believe Temples in a region retain current followers (you need a temple to keep your followers) and get new followers from within the region.
Shrines attract followers from neighbouring regions. I believe it's something like that. There's a whole strategy in placing these temples/shrines just right so you don't waste unnecessary gold
But don't ask me, because I never really got into it.
And obviously, the higher your oratory, the more followers you can reach and convert. I think it's easier to just preach, which will gain you skill as well.
*Awaits Vita to enter*