And we don't have any evidence that Holy Water made by someone without True Faith powers works at all. Harry's is all supplied by Father Forthill...who is a True Believer. In fact, due to Harry's discussion of why Holy water works (infused with a charge of positive energy) that actually makes good metaphysical sense, too.
And being a True Believer is easily as rare as True Magic.
Actually, we do not have any hint that making Holy Water has anything to do with Faith powers...
True believers are the pinnacle of the power that Pure Faith can generate, and i'd allow any True Believer to make Holy water, but it's not a prerequisite.
It is Faith and Holy stuff and all, but basically every Priest can make it, it doesn't even matter which religion he or she follows.
So even if True Believers were as rare as true Magic users, which i don't think they are, Holy water/Stuff would be much more common.
Personally i'd have built the Denarians with a 3 point catch. +2 for availability +1 for researchable (and that would be more to find out what they are than finding the catch... once you know they are fallen angels the leap to holy stuff as a catch is quite easy).
But thats just me.
So, now i'll stop dragging this into a discussion about catches. That's not what the OP wanted.
@OP
Northern religion is something that has been on the descent for a long time. You could consider something along the lines of "
Child of Times long past" as an aspect. Maybe he grew up in a mythical village without all that technical stuff, the huge crowds of people, and the generally high pace of modern life. Now he's supposed to learn the ways of the modern world... That would make him awkward in our society and make the thees and thous you wanted quite fitting.
Obviously that would be an aspect prone to change during his development. Maybe into something like "Keeper of the old ways" to denote that he now has come to grips with the modern world, but still clings to the Old Ways of Honour, Hospitality and the like.
But that's planning a bit far ahead I think.