Will there be maps in dungeons?
Yes, the mini-map will display your immediate surroundings and it will function just like it does anywhere else in the world.
Are there areas that must be unlocked by a key?
Yes, but if you have a wow power leveling Rogue in your party, it can use its lockpicking skill in case you find yourself without the proper key. There are also puzzles that require players to locate the proper key to open a dungeon.