Can I see famous NPCs such as Thrall?
There are various famous characters in the world for you to discover! Make sure you capture a screenshot with them!

Can you attack NPCs/shopkeepers?
You cannot attack NPCs and shopkeepers in your own faction. However, you can attack NPCs and shopkeepers from the opposing side. Keep in mind that NPCs typically reside in enemy towns. In PvP realms, enemy players will be able to attack you if you enter their towns. On normal realms, attacking an NPC or shopkeeper will flag you for PvP and enable enemy players to attack you.

Do NPCs remember if you talked to them before?
For quest purposes, yes, NPCs do remember if you've talked. This helps them keep track of your progress for quests they have given you.

Do NPC merchants close up shop at night?
No, however there will be wandering merchants that might not always be where you last saw them.

Do shopkeepers have a limited supply of items?
Yes and no. Common items are always in supply. However, some shopkeepers sell uncommon items that may or may not be in stock when you visit their stores.