I was thinking about having Jorge and Jan (the two grogs who accompanied the magi during the initial visit) join the new covenant. They're mute and fairly dull, but competent enough to guard the magi.
The covenant might be able to support one or two additional grogs (if they double up as laborers when staying at the covenant), as well as a covenfolk or two for menial tasks (cleaning and cooking), but that's about it for now.
The House Rule for libraries was updated a little while ago. A scriptorium is still useful to produce new books or make copies, though in an abstract way. Will you place it in the regio (safer) or outside with the brewery (better light)?
Each sanctum will be outfitted with some basic furniture, so a place to sleep and study is a given, though it is a bit warm in the caves.