As I understand it and Egregore is formed of a group mind. It is a spontaneous formation and feeds on the energy created by the group, It will dissipate into hibernation with time if the group disbands. I also have a feelin the egregore is why some feel energy in place on the land that hasn't hosted the original group that charged the space to begin with in
The Servitor sounds very similar to a Fetch. A thought formed into a creature to carry out a task. When forming a fetch it is given a span of time to accomplish this, generally from moon to moon. If it is to remain active for a longer period than that, you request that it return for care and feeding, recharging and back to the astral for another moon span.
I don't work with the Servitor because they do sound a bit more complicated and possibly troublesome. A Spirit Guide however, is there to guide, protect and serve your spiritual knowledge while you trod this earth path. You may even have more than one. They don't ask for anything, yet acknowledgement and an occasional treat is nice to form a strong connection.
Ps about witchcraft being a doctoral ship is a start,
this process of learning and fine tuning never ends.