Q15: In MM1 it doesn't say if a Dragon's DR are extraordinary or supernatural, nor the ability to consider their weapons as Magic to overcome this DR.
Q16:: AMF has a 10' radius; if a Dragon casts the spell, does the spell cover only a portion of him, or the spell emanates 10' from every side of the Dragon?
DR is a tricky subject, but in general, this is how it breaks down:
DR/damage type (e.g. slashing): Extraordinary
DR/Magic: Supernatural
DR/admantine: Extraordinary
DR/material (other than admantine): Supernatural (lycanthropes are a noteable exception here)
DR/Epic: Supernatural
DR/--: Extraordinary
AMF, on the other hand, is extremely vague on how it works with large creatures (actually, emenations in general), but it's easiest to figure everything out if it's 10ft from the skin of the caster, so it works the same regardless of who casts the spell.