Also, this is probably not black book related but wikis are listing the following 'Blessings'. Temporary or full time passive?
Blessing of Azura — Resist 10% of magic.
Blessing of Boethiah — One-handed weapons do 10% more damage.
Blessing of Mephala — Prices are 10% better.
Regarding these blessings, I believe they are temporary blessings. You can access all three in the anscestrial temple in Raven Rock at the respective shrines for Mephala, Azura and Boethiah. They are similar to the temporary blessings you receive when visiting the various shrines to the divines in Skyrim (Mara, Arkay, etc.)
Regarding the black books: I have yet to really explore Apocrypha. I know that reading the various books leads you to different parts of the realm, and reading them again will send you back to Solstheim, but how do you attain the various powers? Is it just a matter of exploring the various regions of the realm that each book grants access too? And at the end you come upon the knowledge in book form?