I think that 2051 sounds good to me, I wanted it in the future to add some commentary about the world/church . . . Since the church is progressively moving below the equator, I am thinking the hero is either South American or African, and perhaps the setting is the other. Maybe an African missionary working in SA, or a South American missionary working in Africa. If I am thinking Catholic, probably the heavily Catholic nations in SA make more sense (Brazilian? Argentine?) . . . maybe the Protestant is a native African . . .
How do Catholics do missionary work? I actually don't want my hero to be a priest, but rather a monk or brother . . . do they do missionary work -- like Mother Theresa and the Sisters of Charity, but men? How structured is it? I would like this guy (gonna be a guy, even in 2051 my future Catholic church is not ordaining women) to be sort of solo, maybe a small brotherhood, or he is actually doing solo missions work apart from the order? Could he do baptisms and exorcisms and give communion? I need to do a little research on this, although the future setting gives me some leeway here if this would not be possible in 2006 maybe it will be in 2051.
I am thinking the vampire dude was involved in the spiritualist movement (seances, mediums, etc . . . ), which was at its peak in the late 1900s and early 2000s . . . . his parents involved? I want him to be in business, and the stock market crash of 1929 causes him to contemplate suicide, at which point the demon approaches him . . . and off the story goes!