Is it possible to know the number of total users of christianity.stackexchange.com?
I went around the site but couldn't see it.
In case there isn't: which are the reasons of this choice?
If you look at the sidebar here, you'll see a list of reputation levels and the number of users at or above each level. At the moment, there are 1,451 users with at least 1 reputation (which is basically everyone).
The Users page is a 9 x 4 grid of users and there are currently 40 pages since the last page isn't necessarily full, I'd put the site at somewhere between 1440 and 1480 users.
Not sure why I bothered to answer this since El'endia says the same thing, but what the hey, it's 5:00 and I'm going home.