Board Thread:Warhammer 40k General Discussion/@comment-6134883-20130417202949/@comment-6134883-20130423181355

Full Sisters whether Hospitaller, Dialogus, Framulus or Militant are of course recruited from birth. It seems to me at least possible that some accept adult lay sisters who play the same role as Chapter Serfs do for the Space Marines.

I believe the Brides of the Emperor numbered some 10,000 sisters when they turned against Vandire (at least that what the wiki says). Presumably further sisters were recruited as the new orders were established. Again according to the wiki a preceptory houses a thousand sisters; a commandery 100 (which sounds like the equivalent of chapters and companies) but there are some indications that Orders are not limited to a single preceptory. As something like a dozen orders are listed and probably more exist I suspect your estimate is on the low side.

The different branches of the sisterhood seem to work closely together. Sisters Hospitaller provide medical services, but why a Canoness would need a Sister Dialogus on hand escapes me. Sisters Framulus probably provide valuable intelligence and political backing for militant operations. Between the lot of them the Adepta have their finger in every pot in the Imperium; Military; aristocratic government; Inquisition; probably the Mechanicus (via the Dialogi translators)... Better look out guys the Sisters might OWN you.