I'll just pitch some ideas for this, alright?
PMD: Sun
1. Dayspring Village
2. Sunshine Shores (First Part) followed by Daylight Den (Second Part)
PMD: Moon
1. Eventide Town
2. Moonlight Meadow (First Part) followed by Crescent Cavern (Second Part)
3. I would first think of a 'plot' for the first dungeon to prevent getting overwhelmed by the amount of names.
4. Eh, Players or NPC's?
5. Again, Players or NPC's?