I remember, but I try to always share my work for other people that come to this thread.
1. Sure. I imagine you can place it at the very top of the Quest list though.
2. I imagine Quest space is limited. Multiple Quests may be necessary to get around this limitation. Perhaps you could have 4 Quests in total and divide the ~16 Journal Entries among them. "Journal Entries 1 - 4", "Journal Entries "5 -8", etc. Color coding the text could help the user distinguish between different tips if you're concerned about the "wall of text" effect.
I found something that made things potentially easier. I've read that by setting the spellbook's minimum and maximum spells the same number, it arranges the spells inside the way it's being arranged in the spell list. I don't know if it will stay that way indefinitely but if it does, that solves the arrangement issue.
Considering the space and navigation with the quest, spellbook+passive ability seems the easiest solution. I can even put in there a second spellbook for more space. With this solution, these are the trigger bits are related:
1. Picking up the first journal fragment should give the player the spellbook where the rest goes. I'm guessing a boolean checking for the first journal solves it.
2. Having all fragments inside in disabled form, enabling them when the player find the associated journal fragment is the best way to manipulate things inside spellbook, rather than actually adding the passive ability/fragment to them, right?
3. The item that adds/unlocks each fragment is called "journal fragment". It's basically a powerup book with removed powerup. Since each area holds a specific journal fragment, not a "pick one up and unlock the next", I'm guessing I need one fake powerup book for each fragment in the editor.
4. Whenever I design a trigger, the thing comes to my mind is player who's goofing around to see if he can break it (I did this before). In this case, the player may drops the fragment on the ground, so it's technically not in his possession. I did this in the blood elf campaign with the ring of the archmagi. I think it gave the item to the hero that picked it up then removed the item from the ground. I believe the enable fragment x for player 'user' should still unlock the journal properly although I'm not sure what happens if you drop the spellbook, cross to a different map, pick up the fragment then return to the previous map. Would that cause duplication?
5. Is there a condition that checks for "player owning an item-type" (aka the spellbook)? It may be stashed or not held by the hero who picks up the powerup, so I need to make sure the spellbook won't duplicate because the game checks for the particular hero's inventory.