1) I completed the Quest Spicing Things Up and sold the necklace to spice trader Jethro. After that, I completed forgotten lore, but now I can't access the other areas of the great library or do the quests The Lost Coven or Secrets of The Dead. You're supposed to be able to access the other areas of the library after completing Forgotten Lore, but I think that access to the library technically requires 15 reputation with the loreseekers and since I completed Spicing Things Up before doing Forgotten Lore (and sided with the golden hand) I can't access the library....and since there aren't any other quests to raise my reputation with the Royal Loreseekers, I guess I'm stuck.
One of my lower-level characters has +13 rep with the loreseekers and can access the whole library. I believe the requirement is +10 rep and having completed forgotten lore.
If you gave all four books to the Golden Hand, dropping your reputation to +9, you'll need to complete The Mathrisian Codex
. This will bump your rep to +14, letting you access the library and complete The Lost Coven.
2) sometimes I don't gain much (or any XP from killing enemies)
Spawned enemies give 1/10th the xp. This makes places like the Deadwood and Mercian Royal Crypt dangerous without making them overpowered grinding spots for clerics.