An important belief for night hags, and a theme we might wish to play up for this project, seems to be "In weakness, strength." Night hags gain power through rituals that debase and weaken themselves as well as others, and display weakness as a habit. In part, this is a deception to hide strength -- but in part the weakness is real, and is a source of power itself. What strength they have, comes from manipulation: the items they make and the allies they wield.
Consider a hag's powers. Her innate abilities are shapechanging, spreading a disease, a sense of alignment, a nose for magic, a bit of force throwing, and a knack for robbing simple foes of strength and consciousness -- and her spell-like abilities are nothing that can't be learned by a wizard or cleric practically fresh out of training. And yet, with the investment of a hundred larvae and a month's work, a hag can walk the Ethereal with a facility unrivaled by a human spellcaster anywhere short of the height of his powers, through the use of her heartstone. All hags are expert riders and many own nightmares, which at their mistress' command can launch themselves into the Astral as well.
Night hags can transform other creatures -- debasing them, and usually making them individually weaker in some sense, but paradoxically empowering them. The creation of a broodswarm robs a hag of life force, being created in a painful ritual in the pits of Woeful Escarand in the Abyss, and turns hundreds of manes into even weaker, tiny demons, but creates a swarm entity with far subtler abilities... one slavishly loyal to her.
And in plain sight there is also the hag's favored aspect: an old woman. What weaker, frailer entity can there be, short of a babe in arms? So in this form she hides, her machinations in society hidden behind a veil of helplessness and the regard that society gives its elderly.
And why, if a society doesn't respect its elderly and its women... so much the better for the hag's true goals. Here's one way the theme of "In weakness, strength" could see some development.
-----
The Sisterhood of Lenience is a small, mostly rural religious tradition. It especially flowers in areas with strict ideas on gender roles. Lay members are the women of the community, and the creeds are passed on in a wise-woman tradition from the elder to the younger members. The philosophy's primary moral teachings are humility, adaptability, patience, and quietly accepting events as they come, all traits that the major religions of the region tend to view as eminently suited for women. Indeed, the faith has a reputation for taking "wild girls" in hand and turning them into upstanding members of the community. It has neither temples nor a substantial clergy; spellcasting priestesses are rare (younger ones take vows to remain unmarried, though more often older widows become priestesses), and there certainly is no paladin order. Congregational gatherings are in secluded natural areas, and the holy rituals of the faith are performed by the clergy in private rather than public ceremonies. Female-aspected moon imagery is frequently invoked in the few ceremonies that are undertaken in public, mostly dealing with birth, a woman's coming of age, and the occasional burial rites.
Full Sisters know more of the truth: the Sisterhood is a front for the study of arcane lore. If the innocuous social gatherings and thin veneer of moon worship fail to interest a girl who rebels at the notion that she is supposed to remain passive in the face of hardship, or chafes at her limited opportunities to pursue formal study in a profession (or, better yet, an adventuring class), a Sister approaches her and sounds her out as to interest in amassing a little personal power. With any luck, she is eager to learn how to pay back those who have been stifling her, and thrilled with the prospect of secret knowledge.
These Sisters are not given public priestess status, but are inducted into the Hidden Order in a secret ceremony. From there, they begin a study of a primitive, intricate sort of magic indeed: incantations. These magical workings are available to anyone who cares to make the attempt, without the need for a mage's apprenticeship or a sorcerer's heritage, making the basic incantations a swift road to eldritch power. The Sisterhood has a great store of these suitable for many purposes, most of them with a vengeful, tricksome, or aggressive touch. In return for knowledge, these hidden Sisters are given tasks for the Sisterhood -- collecting empowered materials, swaying the mind of this or that local official, or seeing to it that a nosy cleric is "dissuaded" from pursuing further investigations that threaten to expose the inner circles. As a student learns more incantations and advances in her skills, she becomes more and more tied to the Sisterhood, and often begins delving into incantations with darker procedures and purposes.
A true priestess in the Sisterhood has taken to these tasks with a will. Particularly promising candidates have figured out that the pliability the Lenient Sisters preach prepares the ground nicely for more sinister influences to work their will without opposition. Those who seem comfortable with this are deemed open to learning the real truth of the order, in exchange for greater magical power, useful if subtle wealth, and temporal influence. This truth is that the Sisterhood is a hag cult. Some of those elder members really are old women; others are night hags, extending their influence on the Prime Material. The innocuous preaching of the cult lulls the authorities, and encourages apathy in the face of evil, which feeds larvae to the Waste. If a hidden Sister is willing to become a true cleric of Cegilune, then at midnight on the night of the new moon she can take the secret vows that pledge her soul to the Queen of the Night Hags. Priestesses can't be married, and most farm girls are by that age, but widows are accepted....
This is really, really cool.
Any chance you turn this into an adventure outline for Chapter 7: Dreams out of hell?