A Book of Shadows (BOS) is where I record my spells while I treat my grimoire like a journal for my spiritual path. There's no set rules as to what you use the books for so you can do what you want with them. I call my BOS a Book of Spells.
If you want long life for paper use cardstock paper as it's acid free. I haven't seen any other kind of paper labelled as such but any paper that's acid free is a good choice for longevity. Cardstock is also a bit thicker compared to regular looseleaf paper.
As for ink, you can get pens that contain archival ink which lasts longer than other inks. I got a set at Michael's.
As for my own books, I have a combination of paper and computer. The paper is a mix of binders, notebooks and looseleaf paper that I have out so I can take quick notes. On the laptop I use WordDoc as it's a lot easier for me to add and change things around that I can't do on paper plus I can decorate it.
If you're going to draw and such in your BOS and/or grimoire, I suggest you get a spray can that's specific for covering and protecting pencil drawings so they don't smudge on other paper. I'm not sure if it'd work on paints so check the labels. I think the can is a fixative which I saw in Michael's.
"The Children of God were moulded by the Hand of God which is called Awen..."
The Kolbrin Bible, chapter 5, vs 1
"But ask now the beasts, and they shall teach thee; and the fowls of the air, and they shall tell thee:
Or speak to the earth, and it shall teach thee: and the fishes of the sea shall declare unto thee."
Job 12: 7 and 8 (KJV)