Can a monk use a quarterstaff 2-handed and get a bonus unarmed strike? also, does the unarmed strike add dexterity mod to dmg?

@CoreyBatieCan a monk use a quarterstaff 2-handed and get a bonus unarmed strike? also, does the unarmed strike add dexterity mod to dmg? I’d allow it – monk in my game yesterday described it as a kick or headbutt

— Mike Mearls (@mikemearls) October 4, 2014